THE INFLUENCE OF RESIDENTIAL WATER TANKS ON WATER CONSUMPTION: A CASE STUDY FROM PALMAS, TOCANTINS, BRAZIL

Water losses in a water distribution system refers to the volume of water produced but not consumed (real loss), or consumed but not charged (apparent loss). The International Water Association (IWA) has a method to quantify and identity water losses through the water balance. However, quantifying the apparent loss to compose the water balance can be a challenge. Although installed flowmeters are essential to monitor consumption, they are not enough to estimate apparent loss. For instance, if the meter is operating out of the correct range, it represents an apparent loss that is difficult to evaluate. Among other causes, in residences where private water tanks are used to store water, the use of float valves can cause higher under-measurements. This indirect water feed is the most common case in Brazilian residences and led to this study, based on the analysis of two years consumption data from a district meter area of Palmas, Tocantins, Brazil. The database presents consumption information for 183 directly fed properties and 102 indirectly fed properties, flowmeter operating range and the size of storage, if present. Consumption patterns according to the presence and size of storage were evaluated and showed that the larger the storage the higher the consumption. The data was also analysed statistically by the two-sample t-test and showed that customers without a water tank consumed, on average, 13% more than those with a water tank. When replacing flowmeters, water companies should prioritize customers with water tanks due to the largest investment return. By understanding the available consumption data, water companies can estimate and possibly reduce apparent water loss, by adopting the most adequate measures.