Total Water Withdrawal Research Articles

A new case for promoting wastewater reuse in Saudi Arabia: Bringing energy into the water equation

Saudi Arabia is the third-largest per capita water user worldwide and has addressed the disparity between its renewable water resources and domestic demand primarily through desalination and the abstraction of non-renewable groundwater. This study evaluates the potential costs of this approach in the industrial and municipal sectors, exploring economic, energy, and environmental costs (including CO2 emissions and possible coastal impacts). Although the energy intensity of desalination is a global concern, it is particularly urgent to rethink water supply options in Saudi Arabia because the entirety of its natural gas production is consumed domestically, primarily in petrochemical and desalination plants. This burgeoning demand is necessitating the development of more expensive high-sulfur gas resources that could make desalination even pricier. The evolving necessity to conserve non-renewable water and energy resources and mitigate GHG emissions in the region also requires policy makers to weigh in much more considerably the energy and environmental costs of desalination. This paper suggests that in Saudi Arabia, the implementation of increased water conservation and reuse across the oil and natural gas sectors could conserve up to 29% of total industrial water withdrawals at costs recovered over 0-30 years, depending on the specific improvement. This work also indicates that increasing wastewater treatment and reuse in six high-altitude inland cities could save a further $225 million (2009 dollars) and conserve 2% of Saudi Arabia's annual electricity consumption. By these estimates, some anticipated investments in desalination projects could be deferred by improving water efficiency in industry and prioritizing investment in sewage and water distribution networks that would ensure more effective water reclamation and reuse. Simultaneously, such initiatives would conserve non-renewable natural gas resources and could help prevent the lock-in of potentially unnecessary desalination infrastructure that is likely to become more energy and cost efficient in future.

U.S. Energy Security and Water: The Challenges We Face

U.S. Energy Security and Water: The Challenges We Face

黑河中游取水总量控制风险管理研究

取水总量控制是通过取水量的合理分配和总量控制，实现流域经济社会和生态环境的协调发展。黑河是我国较早实施取水总量控制的流域之一，由于上游来水、区域取水以及用水等过程的不确定性，黑河中游取水总量控制系统不可避免存在着风险，有必要开展相应的风险管理研究。本文结合黑河中游实际情况，从黑河中游取水总量控制的风险因子出发，构建了黑河中游取水总量控制风险评价指标体系，并对风险进行了估算和分析。结果表明黑河中游的取水总量控制风险处于可控状态，但中游的农业和生态用水受到一定的限制。并辨识主要致险和承险因子，提出相应的风险管理措施，为取水总量控制在黑河中游的实施提供指导。 Total water withdrawal control is able to realize coordinated development of the social economic and ecological environment through the reasonable distribution and total amount control. The HeiheRiveris the early implementation of total water withdrawal control. Due to the uncertainty of flow runoff and water demand, the risk of total water withdrawal control in the middle of Heihe River reach is objectively exist, and the corresponding risk management research is also necessary. Based on the analysis of the risk factors, combining with the actual situation of the middle of Heihe river reach, the risk evaluation index system of total water withdrawal control was proposed and the risks were analyzed. The results show that the risk level of total water withdrawal control in the middle Heihe River reach is in a controllable state, but the agricultural and ecological water use are limited in certain extent. The main risk factors and counterforce factors are given which could provide guid- ance for risk management and implementation of total water amount control in this region.

Impact of water withdrawals from groundwater and surface water on continental water storage variations

Humans have strongly impacted the global water cycle, not only water flows but also water storage. We have performed a first global-scale analysis of the impact of water withdrawals on water storage variations, using the global water resources and use model WaterGAP. This required estimation of fractions of total water withdrawals from groundwater, considering five water use sectors. According to our assessment, the source of 35% of the water withdrawn worldwide (4300km3/year during 1998–2002) is groundwater. Groundwater contributes 42%, 36% and 27% of water used for irrigation, households and manufacturing, respectively, while we assume that only surface water is used for livestock and for cooling of thermal power plants. Consumptive water use was 1400km3/year during 1998–2002. It is the sum of the net abstraction of 250km3/year of groundwater (taking into account evapotranspiration and return flows of withdrawn surface water and groundwater) and the net abstraction of 1150km3/year of surface water. Computed net abstractions indicate, for the first time at the global scale, where and when human water withdrawals decrease or increase groundwater or surface water storage. In regions with extensive surface water irrigation, such as Southern China, net abstractions from groundwater are negative, i.e. groundwater is recharged by irrigation. The opposite is true for areas dominated by groundwater irrigation, such as in the High Plains aquifer of the central USA, where net abstraction of surface water is negative because return flow of withdrawn groundwater recharges the surface water compartments. In intensively irrigated areas, the amplitude of seasonal total water storage variations is generally increased due to human water use; however, in some areas, it is decreased. For the High Plains aquifer and the whole Mississippi basin, modeled groundwater and total water storage variations were compared with estimates of groundwater storage variations based on groundwater table observations, and with estimates of total water storage variations from the GRACE satellites mission. Due to the difficulty in estimating area-averaged seasonal groundwater storage variations from point observations of groundwater levels, it is uncertain whether WaterGAP underestimates actual variations or not. We conclude that WaterGAP possibly overestimates water withdrawals in the High Plains aquifer where impact of human water use on water storage is readily discernible based on WaterGAP calculations and groundwater observations. No final conclusion can be drawn regarding the possibility of monitoring water withdrawals in the High Plains aquifer using GRACE. For the less intensively irrigated Mississippi basin, observed and modeled seasonal groundwater storage reveals a discernible impact of water withdrawals in the basin, but this is not the case for total water storage such that water withdrawals at the scale of the whole Mississippi basin cannot be monitored by GRACE.

Water consumption in Barcelona and its regional environmental imprint: a long-term history (1717–2008)

We present the evolution of urban water withdrawal and consumption of Barcelona from the eighteenth to the twenty-first centuries. The boundaries of the urban system have been set into the limits of the current municipality, adjusting the data of earlier periods to include the estimated consumption in former municipalities aggregated to the city. Different sorts of water flows have been either recorded or estimated from scant and indirect information, such as local groundwater extractions obtained from a hydrological model calibrated with historical data on variations in the water table. The changes experienced in catching infrastructures, the regional ecological imprint of the domestic or industrial water consumed together with the rates of growth in population, economic activity and water intensity have been taken into account as driving forces. The series obtained reveal an overall increase in accessibility to safe freshwater, and a corresponding extension of water terrestrial imprints of Barcelona over the Catalan river basins, up to the peak reached in 1967–1970 both for per capita and total water withdrawn. The subsequent downward trend, mainly driven by a lesser water intensity of the local economy, a halt in population growth, and a recently link to the emergence of a New Sustainable Water Culture in Catalan society, stands out against the alleged need for new transfers from farthest basins such as the Ebro or Roine rivers.

Analysis of agricultural sustainability: A review of exergy methodologies and their application in OECD countries

This article proposed the combination of cumulative exergy extraction from the natural environment and extended exergy analysis to analyse international environmental performance in agricultural production. The unified approach allowed the cumulative analysis of total extraction of all types of resources and services from the ecosystem in agriculture. The analysis, therefore, enabled a more accurate comparison of the environmental performance of different countries or systems based on different indicators of sustainability. The application was conducted for 29 OECD countries for the years from 1990 to 2003 with some important findings. First, the organic contents in topsoil, feed and total water withdrawal were the three types of resources that agricultural production extracted most from the environment. Second, during the 14 years surveyed, the efficiency of using exergy in the livestock sector was much lower than the efficiency in the crop sector. Third, the environmental loading of economic investment had increased slightly, implying a minor increase in the pressure on the environment overtime. In addition, the empirical study on OECD countries confirmed that rankings varied widely based on different indicators. The empirical results gave some evidence to support the use of non-renewability yield ratio, firstly defined in this paper, because the rankings based on this indicator was more consistent with many other indicators.

Water Use at Pulverized Coal Power Plants with Postcombustion Carbon Capture and Storage

Coal-fired power plants account for nearly 50% of U.S. electricity supply and about a third of U.S. emissions of CO(2), the major greenhouse gas (GHG) associated with global climate change. Thermal power plants also account for 39% of all freshwater withdrawals in the U.S. To reduce GHG emissions from coal-fired plants, postcombustion carbon capture and storage (CCS) systems are receiving considerable attention. Current commercial amine-based capture systems require water for cooling and other operations that add to power plant water requirements. This paper characterizes and quantifies water use at coal-burning power plants with and without CCS and investigates key parameters that influence water consumption. Analytical models are presented to quantify water use for major unit operations. Case study results show that, for power plants with conventional wet cooling towers, approximately 80% of total plant water withdrawals and 86% of plant water consumption is for cooling. The addition of an amine-based CCS system would approximately double the consumptive water use of the plant. Replacing wet towers with air-cooled condensers for dry cooling would reduce plant water use by about 80% (without CCS) to about 40% (with CCS). However, the cooling system capital cost would approximately triple, although costs are highly dependent on site-specific characteristics. The potential for water use reductions with CCS is explored via sensitivity analyses of plant efficiency and other key design parameters that affect water resource management for the electric power industry.

Energy and Water Programs within the United States Department of Agriculture

The United States Department of Agriculture (USDA) is one of the nation’s oldest Federal departments. It employs more than 100,000 people whose work touches the lives of every American in various ways every day. It is one of the most complex departments in the Federal Government, with more than 300 programs that spend more than $75 billion each year to help lead and manage a variety of food, agriculture, natural resources, and related programs. The USDA goals and objectives, and the implementation of its programs, are sound public policy based on the best available science. USDA works with individuals, agricultural and natural resources organizations, and units of government throughout the U.S., and in many other countries throughout the world, to enhance economic opportunities for agricultural producers and rural communities, to protect the nation’s food supply, to improve nutrition and health, and to protect the nation’s natural resources and environment. Energy and water programs are critical components of the USDA. Agriculture in the U.S. is both a major consumer and producer of energy, with crops, forests and livestock requiring energy use for all aspects of production in the field, transport and processing, and conversely, the use of biofuels as a growing source of energy throughout the country. Irrigation is the largest user of freshwater in the U.S. and accounts for about 65 percent of total water withdrawals, excluding water used for thermoelectric power (Schaible 2004). Irrigation is critical in the U.S. as nearly half the value of all crops sold comes from the 16 percent of harvested cropland that is irrigated (Schaible 2004). Because energy and water are so critical for agriculture, the USDA strives to meet emerging issues by supporting the development and use of new technology for increased energy production and energy conservation, and by providing water supply information along with technical and financial assistance to improve the management decisions affecting both water quantity and quality. This paper provides a brief overview of the many energy and water programs managed in the USDA.

Integrated Policy and Planning for Water and Energy

We are faced with chronic water and energy vulnerabilities. Some argue that we will face two crises in the 21st century: a water crisis and an energy crisis (Brown 1998, 2003, Flavin 1999, Feffer 2008). Water will become increasingly scarce as water tables drop due to over-consumption and water quality will continue to deteriorate as a result of excessive contamination. Further, the present energy regime’s dependence on non-renewable sources has added considerable stress to the environment, including the prospect of climate change (Intergovernmental Panel on Climate Change 2007). We are amidst a situation where we could be easily blamed for compromising the ability of future generations to meet their needs. This paper first briefly describes a need for understanding the integrated considerations of water and energy in resource planning, especially during droughts. After introducing a conceptual framework of the water-energy integration, this paper reviews the results of a national survey of energy and water departments to see how these synergic benefits are explored at the state level. Lessons learned from our case studies serve as useful guidelines for state water-energy planning and program development. Finally, as an example case of the water-energy nexus, the concept of desalination is introduced with its implication on energy demand.

Water withdrawal for brackish and inland aquaculture, and options to produce more fish in ponds with present water use

This paper reviews freshwater use in inland and coastal pond aquaculture, and focuses on options to increase productivity while reducing water use. Total freshwater use depends on system-associated and feed-associated water losses. System-associated water losses depend on total area, evaporation, infiltration and water replacement. About 8,750,000 ha freshwater and 2,333,000 ha brackish water ponds are in use today. Total water withdrawal in freshwater aquaculture is estimated at 16.9 m3/kg production, representing 429 km3/yr, which is 3.6% of flowing water globally. Infiltration and replacement water recharges aquifers; if these losses are clean, their re-use decreases aquaculture-related water withdrawal by nearly 60%. A further reduction in freshwater use in aquaculture can come from intensification and aquafeed development. The goal should be to feed the pond, not the fish. A tripling of average pond production should be possible, without increasing total freshwater use. Such improvements will also benefit brackish water aquaculture, which could in turn further reduce freshwater use by increasing the productivity of saline systems.

An integrated model for the assessment of global water resources – Part 2: Applications and assessments

Abstract. To assess global water resources from the perspective of subannual variation in water availability and water use, an integrated water resources model was developed. In a companion report, we presented the global meteorological forcing input used to drive the model and six modules, namely, the land surface hydrology module, the river routing module, the crop growth module, the reservoir operation module, the environmental flow requirement module, and the anthropogenic withdrawal module. Here, we present the results of the model application and global water resources assessments. First, the timing and volume of simulated agriculture water use were examined because agricultural use composes approximately 85% of total consumptive water withdrawal in the world. The estimated crop calendar showed good agreement with earlier reports for wheat, maize, and rice in major countries of production. In major countries, the error in the planting date was ±1 mo, but there were some exceptional cases. The estimated irrigation water withdrawal also showed fair agreement with country statistics, but tended to be underestimated in countries in the Asian monsoon region. The results indicate the validity of the model and the input meteorological forcing because site-specific parameter tuning was not used in the series of simulations. Finally, global water resources were assessed on a subannual basis using a newly devised index. This index located water-stressed regions that were undetected in earlier studies. These regions, which are indicated by a gap in the subannual distribution of water availability and water use, include the Sahel, the Asian monsoon region, and southern Africa. The simulation results show that the reservoir operations of major reservoirs (>1 km3) and the allocation of environmental flow requirements can alter the population under high water stress by approximately −11% to +5% globally. The integrated model is applicable to assessments of various global environmental projections such as climate change.

Spatial Analysis of Water Use in Oregon, USA, 1985–2005

Water use patterns are not distributed evenly over space and time. Determining the amount of water used within a region, as well as the various ways in which water is used is important for making adequate and sustainable water management policies and determining future water availability. We examined differences in spatial trends in Oregon freshwater use (total, municipal, and agricultural water withdrawals), by county, between the years 1985 and 2005. We also explored biophysical and socioeconomic factors that explain spatial patterns using Moran’s I, local index of spatial autocorrelation (LISA), and spatial regression models. There was a moderate positive spatial autocorrelation among counties that had similar total and irrigation withdrawals. LISA analysis identified hot spots between certain arid agricultural counties in the southeastern Oregon and cold spots between certain humid northwestern counties, including within the Portland metro area. Annual precipitation and income are negatively associated with total water withdrawals. Summer temperature and farm size is positively associated with irrigation water withdrawals, while net cash return and income are negatively associated with irrigation water withdrawals. When compared to ordinary least square regression models, spatial error models that take into account spatial dependence provide a more comprehensive explanation of the variations of water use, suggesting that water resource planning and management should incorporate spatial and neighborhood effects to effective manage limited natural resources.

Projection of future world water resources under SRES scenarios: water withdrawal / Projection des ressources en eau mondiales futures selon les scénarios du RSSE: prélèvement d'eau

Potential changes in the availability of water resources are one of the greatest concerns relating to global climate warming. Socio-economic developments will also influence water use and demands. This study was conducted to evaluate potential changes in water withdrawals and availability under various socio-economic and climate change scenarios. In the current paper, which presents the first part of the study, future potential water withdrawals are projected according to socio-economic driving factors under the scenarios A1b, A2, B1, and B2 of the Special Report on Emission Scenarios (SRES), which was released for the Fourth Assessment Report on global warming by the Intergovernmental Panel on Climate Change (IPCC-AR4) in 2000. Total world water withdrawal is currently approximately 3800 km3/year, and will likely exceed 6000 km3/year by 2055, according to all scenarios. Water withdrawal is projected to increase in the future, but change trends largely depend on the socio-economic scenarios. Scenario A2 shows the extreme situation of continuously increasing water withdrawal. The scenario with global cooperation on solutions to social, economic, and environmental issues (Scenario B1) illustrates that society can reach relatively higher economic development by using less water and thus encourages sustainable governance of world water resources. In addition, comparison with other studies is conducted to help us understand the uncertainty range when projecting world water withdrawals according to different methods and assumptions.

Estimating water use of sclerophyllous species under East-Mediterranean climate: III. Tabor oak forest sap flow distribution and transpiration

The annual course of daily transpiration and the hydrological balance of a Tabor oak forest were determined. The study was done in a representative forest within the natural geographical range of the species in the lower Galilee region of Israel. The climate is sub-humid with a rainless dry season from May to October. A partial water balance of a 0.1 ha area supporting an average of 14 trees was calculated from: (a) soil water content (SWC) measured by a Neutron Probe at depths of from 0.2 to 8 m, and (b) daylight transpiration rate measured with sap flow sensors by the heat pulse technique. Soil–bedrock complex water content (%) in the first 2 m of the profile fluctuated strongly between 5 and 20% depending on the season. The water content increased with depth from about 10% at 2.0 m depth to more than 20% at 5.0 m depth. For depths exceeding 5.5 m seasonal fluctuations in water content were negligible and water content ranged from 30 to 35%. After a dry winter, water content generally decreased within the main root zone down to about 2.0 m depth. Monthly changes in water content (mm) were greatest at depths of 0.35–1.0 m. Only minor changes in the soil–bedrock complex water content were recorded at greater depths. After a very rainy winter (2002/2003), decreases in soil–bedrock complex water content in the upper 2 m were much larger than after a dry winter. Fluctuations of soil–bedrock complex water content in deeper regions were larger in the wetter year, probably the result of drainage. Sap velocity was measured at six depths in the sapwood, from 4 to 44 mm, at 8 mm intervals. Sap velocity declined with depth, hence, sap flux density too. Based on sap velocity measurements performed during 4 years, the annual average daily transpiration ( T) was 0.796 mm/day. This sums up to 239 mm during ∼300 days of leaf carriage, i. e. 41.3% of the 578 mm average annual rainfall for the area in the last 50 years. In a relatively dry year (rainfall of 432.7 mm) total water withdrawal from the 8 m soil–bedrock profile was 81% of the annual rainfall; of this amount 69% were transpired by the oak trees (239.0 mm), or 55% of the annual rainfall. In a relatively wet year (annual rainfall 801.4 mm) total water withdrawal was 67%; of this amount 45% would be transpired by the oak trees, or 30% of the annual rainfall.

Hydrogeologic characteristics of the alluvial tuff aquifer of northern Sahand Mountain slopes, Tabriz, Iran

The Tabriz area is a densely populated area of northwestern Iran (more than 1.5 million in population) with a large proportion of its drinking, domestic, industrial and agricultural water supplied from groundwater resources. The average rate of drinking and industrial water use in the city of Tabriz is about 3.45 m3 s–1. The Plio-Pleistocene unconfined alluvial tuff aquifer (about 1,275 km2), the most important aquifer in the area, has been known for many years as a reliable resource. The greatest estimated thickness of the alluvial tuff lies in the Saidabad area, with 350 m thickness. There are 994 deep and 284 shallow active pumping wells and 83 qanats operate in the alluvial tuff aquifer. The total water withdrawal from all these artificial discharge points has been measured at 72, 3.8 and 17 million m3/year, respectively. Analytical and numerical methods have been applied to the constant rate pumping test data from the Saidabad wellfield (eight pumping and three observation wells). The values of electrical conductivity in the groundwater of alluvial tuff aquifer range from 203 to 960 μS cm–1 and bicarbonate type water dominates.

A Pilot Global Assessment of Environmental Water Requirements and Scarcity

This paper presents a first attempt to estimate the volume of water required for the maintenance of freshwater-dependent ecosystems at the global scale. This total environmental water requirement consists of ecologically relevant low-flow and high-flow components and depends upon the objective of environmental water management. Both components are related to river flow variability and estimated by conceptual rules from discharge time series simulated by the global hydrology model. A water stress indicator is further defined, which shows what proportion of the utilizable water in world river basins is currently withdrawn for direct human use and where this use is in conflict with environmental water requirements. The paper presents an estimate of environmental water requirements for 128 major river basins and drainage regions of the world. It is shown that approximately 20 to 50 percent of the mean annual river flow in different basins needs to be allocated to freshwater-dependent ecosystems to maintain them in fair conditions. This is unlikely to be possible in many developing countries in Asia and North Africa, in parts of Australia, North America, and Europe, where current total direct water withdrawals (primarily for irrigation) already tap into the estimated environmental water requirements. Over 1.4 billion people currently live in river basins with high environmental water stress. This number will increase as water withdrawals grow and if environmental water allocations remain beyond the common practice in river basin management. This paper suggests that estimates of environmental water requirements should be the integral part of global water assessments and projections of global food production.

Assuring Water for Food: The Challenge of the Coming Generation

There are many problems facing us on the road to a water-secure future. This paper addresses only one: the need for more water for food production to meet the needs of a population that will increase by some 2 billion before it stabilizes. Irrigation accounts for about two-thirds of total water withdrawals and as much as 80-90% in many developing countries. Of a total of 1500 2 10 6 ha under cultivation, 300 2 10 6 ha of irrigated land provides some 40% of total food production. Expansion in rain-fed areas would mean huge environmental costs, and therefore, a combination of increased efficiency in irrigation, better crop deployment, agricultural research in all areas and changes in dietary profiles will all be needed. As none of these solutions is quick-acting, we must start on all these fronts promptly if we are to manage our water resources wisely.

Discussion of “Optimal Allocation of Water Withdrawals in River Basin” by Jennifer M. Jacobs and Richard M. Vogel

The authors present an objective methodology using flow duration curves and a chance-constrained mathematical programming technique to determine the optimal allocation of streamflow to competing multiple users in a river basin. The discusser feels that the methodology presented by the authors is very interesting and valuable to field engineers and policymakers involved in water allocation decisions. The methodology has merits because of its simplicity, its ease in implementation, and its ability to help in understanding the impact of streamflow availability and user requirements on the streamflow allocation. However, the discusser feels that a few points associated with the formulation and application of the proposed general chance-constrained model for maximizing water allocation in a river basin for productive use must be addressed and clarified before the proposed model can be advocated for implementation in solving real-life problems. STREAMFLOW ALLOCATION MODELS The inequality constraints defined by (2) and (3) in the proposed general chance-constrained model for maximizing water allocation in a river basin for productive use place restrictions on the permitted withdrawal quantity to ensure that water allocation at a site does not exceed its demand and in no case is it less than the existing permitted quantity. In fact, these inequality constraints represent the upper and lower bounds placed upon the amount of permitted withdrawals by users at various sites. Solutions are being sought to optimize total water withdrawals in a river basin to meet demands at various sites with its acceptable streamflow reliabilities. Taking this cognizance, the inequality constraints defined by (6) and (7) become redundant. The constraint set defined by (3) and (4) itself ensures that the decision variables q i and ri are nonnegative, where qi is the permitted withdrawal quantity for site i, and ri is the streamflow reliability for withdrawal i. If allocation is desired on the basis of only flow duration curves (FDCs) and demands at various sites, without putting any restriction of minimum withdrawal permit, solution can be obtained by assigning zero values to pi for all values of i, where pi is the existing permitted withdrawal at site i. The second issue is associated with the range within which the water allocation at a particular site is allowed to take any value during the optimization search process to maximize the total water allocation in a river basin. The constraint set defined by (3) is nothing but the demands requested by various users estimated currently or previously. The constraint set defined by (2) is basically the projected demand by various users in the coming future. This conceptualization has a flavor of scheduling the permitted withdrawals at various sites. Thus, it may be appropriate even to cut down water allocation at some insensitive sites to values less than their existing permits in order to maximize the production function. This is relevant when the reductions are likely to occur in streamflow availability. In such cases, the optimal solution will be primarily based on the FDCs. The sensitivity herein is with respect to production function. In fact, the lower limit on the variable q i

Environmental Heat and Partial Water Restriction Effects on Body Fluid Spaces, Water Loss, Body Temperature, and Metabolism of Holstein Cows

The effects of partial water restriction on metabolism, body fluid compartments, and water balance were measured in seven mature nonlactating Holstein cows at two constant environmental temperatures, 18 and 32C. For 7 days at each temperature, water was restricted to 50% of ad libitum consumption.Partial water restriction at 18C caused a 50% reduction in water loss with a reduction in total body fluid volume mainly from the extravascular fluid compartment. This was followed by a reduction in feed consumption and metabolism. At 32C partial water restriction caused a great reduction in water loss through urine and feces, allowing more of the water to be used for heat loss by vaporization.Partial water restriction, unlike total water withdrawal, did not change the volumes of vascular compartments at either normal or high temperatures. However, animals exposed to normal and high temperatures respond differently to water restriction. At 18C similar percentage reductions (approximately 50%) occur in urine, fecal water, and total vaporization to reduce water loss during water restriction. But at 32C water loss is reduced mainly by reduction of urine and fecal water, rather than vaporization.Comparison between ad libitum animals at the two temperatures showed that heat caused a 15.9% reduction in metabolism. Water restricted cows, compared to ad libitum cows at 32C, showed a 17.0% reduction in metabolism. Results suggest the reduced metabolism is a compensatory mechanism to reduce internal heat production in an environment of high external heat and low water availability. Also, insignificant reduction in blood and plasma volumes produced available fluids for heat loss through vaporization when water was restricted at a high temperature.