“New” Water

Abstract

We are continually inundated with news and views about the demand for water outpacing supply. Our unsustainable development along rivers that do not reach the sea, declining ground water levels, damage to wetlands, high costs associated with acquiring new sources of water, and potential shortages related to global climate change are common news items. In most developed economies, there is little or no unallocated fresh water left to exploit. So, the question becomes: Where do we find “new” water for our burgeoning population? The answer may lie in the treatment of both shallow, brackish ground water and postconsumer water. Recent advances in reverse-osmosis membranes have reduced operational costs and established a linear correlation between total dissolved solids and operational cost of desalination; thus, there is increased interest in brackish water as input source. In the Southwest, the El Paso, Texas, Water Utilities Public Service Board recently dedicated a 100 million L/d desalination plant. Surprisingly, Florida with its high rainfall of more than 100 cm a year and many lakes and rivers is commonly thought of as a water-“rich” state; yet it has more water desalination plants than any other state: the city of Tampa Bay has the largest active desalination plant in the United States and uses brackish water from Tampa Bay. It is estimated that the state of New Mexico contains 16,000 billion m3 (13 billion acre-feet) of shallow brackish ground water (total dissolved solids greater than 500 mg/L and less than sea water, which is 35,000 mg/L). I suspect that development of brackish water aquifers would, in general, have less impact on the ecology than development of fresh water aquifers. That being said, we know little about the extent and chemistry of brackish water aquifers and almost nothing about their boundary conditions. Thus, I propose a federal 10-year sunset assessment of 1‰ per 250 gallons on all the ground water that municipalities extract, or about $1.00 each year for the average household using ground water. It is envisioned that this study would quantify the regional hydrology of these aquifers following the USGS’s Regional Aquifer System-Analysis model for fresh water aquifers. It would also identify any potential deeper formations capable of sequestering desalination concentrate. This small investment coupled with reduced consumption from increased rate changes and conservation measures such as low-flush toilets, low-flow showerheads and watering restrictions will prolong our existing resources and give us time to install the necessary infrastructure. We need to wean ourselves from our “once through, throw it out” philosophy that dominates current water resource management. We also need to reframe the linguistic argument away from “sewerage” or “waste water” toward the more societally acceptable “postconsumer” or “surplus municipal water.” (Remember, it is not a “used” car, it is a “previously owned” car!) Cities will soon no longer have the luxury of passing their used municipal water downstream. “Dilution is the solution to pollution” is a dated and unfair concept of passing water quality problems to the aquatic environment and cleanup expenditures to downstream users. Newly engineered membranes in desalination plants are excellent at removing not only salts but also pharmaceuticals, endocrine disruptors, prions, and other undesirable products left untouched by conventional waste treatment facilities. Combining membrane-treated water with aquifer storage and recovery (ASR) offers some interesting water management possibilities. That is, by recharging refreshed water, which is generally of better quality than native ground water, into aquifers, one can control the blending ratio of refreshed to native ground water in producing well fields. Furthermore, the aquifer provides a unique environment to adjust the temperature and chemistry and continue filtering the recharged water, adding insurance against the transport of many undesirable contaminants. Desalination and ASR are, however, energy-intensive processes; thus, greenhouse gas–free energy is likely to be integrated in any future energy scenario. Currently, approximately 28% of all electrical power generated in the United States is greenhouse gas–free (nuclear 19.3%, hydro 6.5%, biofuels 1.6%, wind less than 1%, and solar less than 1%), so these are likely to be the energy sources for desalination. Because both the membrane and the ASR technologies are mature and well established, development of new water from brackish ground water and postconsumer water could be a rapid and straightforward resolution to many of the domestic and industrial demands of our nation’s water resources well into the future.