Bottom-Up Analysis for Assessing Water Losses: A Case Study

Abstract

The current paper focuses on the assessment of real (physical) and apparent losses in a District Metering Area (DMA) of a Portuguese water utility based on collected data during a leak detection and location survey. Water losses have been assessed by means of bottom-up calculations based on the analysis of minimum night flows in the DMA and extended period hydraulic simulations of the hydraulic system. The analysed DMA is part of a Portuguese water distribution network, covers a 0.7 km 2 area, is predominantly residential (mainly, with domestic consumption), with approximately 6200 inhabitants and a large non-domestic consumer (representing one-third of billed consumption). The DMA has been temporarily isolated by closing ten boundary valves. It has 9.4 km of pipes with diameter from 50 to 300 mm, 589 service connections and 3400 billed consumers. Flow and pressure data have been collected in the DMA input section, during a leak detection survey carried out during an eight-weak period (from 13th October to 13th December of 2004). Data collection frequency was 30 measurements per hour (every 2 minutes). A brief description of the leak detection survey is presented. Water losses have been assessed before and after the leakage detection survey by means of a bottom-up approach based on minimum night flow analysis and dynamic hydraulic simulation of the system. Minimum night flow data, between 2:00 and 4:00, were used for estimating real losses (leakage) based on several assumptions and considerations referred in “Report F - Using Night Flow Data” (WRC, 1994). In order to estimate daily volume of leakage and apparent losses, hydraulic simulations of the system behaviour have been carried out using collected flow and pressure during 24 hours. EPANET was used to carry out the extended period simulation of the system. The bottom-up approach followed can be summarised in a six-step procedure that will be described in the paper. Water losses are assessed before and after the survey. Results have shown that: (i) the leak detection survey reduced real losses (leakage) in approximately 27%, which corresponds to an annual water volume of 130 000 m 3 , despite the seasonal demand variation of 22%: and (ii) apparent losses and unbilled authorised consumption, even after the survey, still represent 33% of total water volume. The balance of the survey was very positive as it reduced real losses in 14.5.m 3 /h which represents a pay-back of 63 500 €/year.