Quick Answer
When sizing cistern systems in arid regions, consider the area's average annual rainfall, population needs, and water storage requirements to ensure a reliable and efficient water supply. A general rule of thumb is to store at least 1,000 gallons (3,785 liters) of water per person. This amount can be adjusted based on climate, water usage patterns, and other factors.
Determining Rainfall Collection Needs
In arid regions, it’s essential to collect and store as much rainfall as possible. A rough estimate for rainfall collection needs in arid areas is to design for a 1-2 inch (25-50 mm) per month rainfall event. For example, in a region with a 1 inch (25 mm) per month rainfall event, a 2,000 square foot (185 square meter) rooftop would require a cistern with a capacity of at least 20,000 gallons (75,708 liters) to store the collected water.
Cistern Sizing Calculations
To size a cistern, calculate the total water demand per day, and then multiply it by the number of days the cistern needs to supply water. For example, if a household needs 100 gallons (378 liters) of water per day and the cistern needs to supply water for 30 days, the required cistern capacity would be 3,000 gallons (11,356 liters). Consider factors like evaporation, seepage, and water losses when sizing the cistern.
Additional Considerations
When designing a cistern system in arid regions, consider factors like water treatment and storage options. For example, a UV treatment system can be used to disinfect water before storage, and a floating intake can help prevent sediment and debris from entering the cistern. Additionally, consider the material and durability of the cistern, as well as any relevant local regulations or building codes.
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