Do household surveys estimate tap water use accurately? Evidence from pressure-sensor based estimates in Coimbatore, India.
Quantifying domestic water use at the household scale is crucial for any policy interventions towards ensuring adequate, equitable and safe water access. In developing country contexts, piped water supply is often one of several sources from which households access water and this is often unmetered. The most common approach to quantifying household water use from multiple sources is through household surveys. But there is no evidence that household surveys accurately estimate water use. This study utilized high-resolution pressure-sensor data as a reference to evaluate the effectiveness of conventional household survey methods through a sample of 82 households in Coimbatore city in South India. The pressure sensors produced detailed, continuous and accurate information on all sources of water accessed through the household storage infrastructure, but they were expensive and intrusive. Compared with pressure-sensor derived estimates of tap water use, household surveys alone fared very poorly. However, household surveys and well-designed water diaries of supply and pumping, coupled with simple one-time field measurements, emerged as a valid approach to quantifying household water use from taps under multiple source dependence.