How to Manage Evaporation Losses in Rainwater Storage?

Reducing Evaporation

To minimize evaporation losses, cover the storage tank with a lid or a tarp. A well-fitted lid can reduce evaporation by up to 90%. Ensure the lid is secure and consider using a UV-stabilized tarp to prevent degradation from sunlight. The tarp should be at least 10 mils thick and have a waterproof coating. For larger tanks, consider using a floating intake valve that draws water from the surface, thus minimizing the exposed surface area.

Preventing Contamination

A first flush device should be installed at the roof inlet to divert the initial flow of water, which may be contaminated with debris, leaves, and other pollutants. This ensures that clean water is collected and stored. A first flush device typically consists of a diverter valve and a float that opens to allow clean water to flow into the storage tank. For a small storage tank, a 1:10 ratio of first flush volume to tank capacity is recommended. For example, a 1,000-gallon tank may require a 100-gallon first flush device.

Storage Tank Maintenance

Regular maintenance is crucial to prevent contamination and reduce evaporation losses. Check the storage tank for cracks, rust, or other damage and repair or replace it as needed. Clean the tank and its components regularly, and inspect the lid and tarp for damage or wear. Consider using a water treatment system, such as a UV filter or a sediment filter, to ensure the stored water is safe for use.