Potential for drinking water savings through rainwater use: a case study in Brazil

Abstract This article assesses the potential for drinking water savings through a rainwater harvesting system for non-potable purposes in a flat. The appliances’ water flows were measured; users made daily notes of water consumption, time of use of each appliance, and the number of times this occurred; and daily readings of the water meter were made over fifteen days. Based on these data, the water end-uses and the average daily consumption were calculated. The measurements showed that the percentage of water for activities that do not require drinking water (toilet flushing, cleaning and washing machine) was 36.5% of the total consumption. Through the Netuno computer programme, the ideal capacities of rainwater tanks were determined for variable and average water consumption. It was found that a 10,000-litre tank provides drinking water savings of 34.8%, fully meeting the demand over 95% of the days. The study showed that, even with a considerable variation in consumption, the ideal capacity of the lower tank and the water savings achieved do not vary significantly when using variable or the average water consumption.