Quick Answer
Calculate household water usage by estimating daily water consumption per person, then multiply that amount by the number of occupants and add allowances for outdoor use, washing machines, and other appliances. This will give the total daily water requirement, which is used to determine the optimal cistern size. Use a safe factor to account for potential water losses.
Understanding Water Usage Patterns
Before sizing a cistern, it’s essential to understand household water usage patterns. Start by estimating daily water consumption per person. A commonly used estimate is 50-100 gallons per person per day. For a family of four, this would be 200-400 gallons per day. Next, add allowances for outdoor use, such as irrigation systems and pool filling, as well as washing machines and dishwashers.
Calculating Total Daily Water Requirement
To calculate the total daily water requirement, multiply the estimated water consumption per person by the number of occupants. For example, a family of four with estimated water consumption of 75 gallons per person per day would have a total daily water requirement of 300 gallons. Add allowances for outdoor use, such as 50-100 gallons per day for irrigation, and 20-50 gallons per day for washing machines and dishwashers. This would bring the total daily water requirement to 370-500 gallons.
Determining Cistern Size
Use the total daily water requirement to determine the optimal cistern size. A safe factor of 20-30% should be applied to account for potential water losses due to evaporation, seepage, and other factors. For example, if the total daily water requirement is 370 gallons, a cistern with a capacity of 400-500 gallons (20-30% larger) would be recommended. This will ensure that the cistern can meet the household’s water needs during periods of low rainfall or when the water supply is interrupted.
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