How Big of a Storage Tank Do You Need for a Rainwater Collection System?

Passive Collection System

• No tank is required for a passive rainwater collection system. Such systems work better in climates with average or above-average rainfall. Soil and mulch are used in such a way as to maximize the benefits of regular rainfall. Special channels and shallow basins are dug directly into the soil, allowing the rainwater to naturally percolate through the soil. Mulch is used around plants to keep them moist and preserve them from the drying effects of the sun.

Purchased Container

• Ready-made rainwater collection barrels are available for purchase. These range in size from 50 to 65 gallons. The arrels come already fitted with lids and screens, as well as a spigot that allows you attach a hose or fill a watering container with the harvested water. Depending on the size of the area you need to water and the amount of rainfall you receive, a single barrel may be enough to meet your needs. If not, a series of barrels may be used by connecting the barrels to one another via tubing or a pipe.

Repurposed Container

• Construct a rainwater collection barrel easily from other less expensive containers. This structure also allows for a different-sized container to be used. The barrel will need to have a fitted top and screen as well as a spigot. Containers that are dark and opaque inhibit algae growth on stored water. Wooden wine barrels as well as food grade plastic barrels or containers can be turned into a rainwater collection barrel.

Larger Systems

• If the rainwater collection system is for a larger, commercial entity or if the system will be filtered and used for regular household water consumption, a larger storage tank or cistern will need to be used. These types can be built either above or below ground and can be constructed from a variety of materials. Estimate the size needed for a system that will supply all household water based on the amount of water used each month and the amount of rainfall that falls each month.