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In this page, we provide a basic overview of the installation of a rain water harvesting tank for garden and landscape irrigation. If you'd like a more comprehensive guide, then we recommend the The Texas Manual on Rainwater Harvesting.
Before you begin, here are the key components:
The leaf catcher/ Leaf eater:
A leaf catcher is a filtration device installed in a rainwater harvesting system, typically at the downpipe or before water enters the tank. It removes leaves, twigs, and other large debris from the rainwater, preventing them from clogging pipes or contaminating the stored water. The catcher typically has a sloped or mesh screen to direct debris away while allowing water to flow through. You will want to clean the leaf catcher on a regular basis.
California Plumbing Code 1602.9.10 - Debris Removal
The rainwater catchment conveyance system shall be equipped with a debris excluder or other approved means to prevent the accumulation of leaves, needles or other debris and sediment from entering the storage tank.
First Flush diverter:
A first flush diverter prevents the initial runoff, which often contains dirt, debris, and contaminants from roofs and gutters, from entering the main tank. It collects and temporarily stores this dirty water, allowing cleaner rainwater to flow into the storage tank once the chamber is full. This helps improve water quality and protects the tank from sediment buildup. A first flush diverter should be emptied after a rain storm.
Watch this video for a visual representation of how a first flush diverter functions.
Overflow
A rain tank overflow is an outlet at the top of the tank that directs excess water away from the tank when it reaches full capacity. It typically channels the overflow to a designated area/flow path or to a swale. The dimensional width of your overflow pipe should be the same as your inlet pipe. The outlet pipe, or spigot/valve where you get water out of the tank, can be a smaller diameter.
California Plumbing Code 1602.9.5.5 - Drainage and Overflow.
Rainwater storage tanks shall be provided with a means of draining and cleaning. The overflow drain shall not be equipped with a shut off valve. The overflow outlet shall discharge in accordance with this code for storm drainage systems.
Swales and rain gardens:
Swales can come in many forms but overall function of a swale to direct runoff in a certain direction.
A bio-swale is a shallow channel filled with organic material such as wood-chips and often planted with plants designed to sequester, filter, and direct rainwater runoff into the soil where it will then help to recharge aquifers. It helps remove pollutants, sediment, and debris from the water while allowing more water infiltration into the soil. (left)
A drainage swale has less permeable materials such as rocks to direct runoff to drain to a specific area. (right)
We highly recommend diverting your overflow into a rain garden or a bioswale.
Tank Cover:
A locking tank cover is important so that children do not accidentally fall into the tank. Do not allow anyone to climb onto the tank.
Dry vs Wet Piping:
Dry piping systems (which we will focus on in the rest of this section) use gravity to direct water, relying on the source of water (the downspout) being higher than the inlet to the tank and the piping having a slope to allow for water to flow freely.
Wet piping systems (which often involve more piping) rely on the idea that water always reaches the same level. Water fills the pipes to make up for the lack of gradient between the downspout and the inlet.
Legal signage and non potable water sign:
For non-residential facilities we recommend signage to ensure compliance with the California Plumbing Code: 1602.9.5.7 which says:
Rainwater tanks shall be permanently marked with the capacity and the language "NONPOTABLE RAINWATER." Where openings are provided to allow a person to enter the tank. The opening shall be marked with the following language: "DANGER-CONFINED SPACE."
Additionally, find below a list of Brad Lancaster's 10 Principles for Designing Rain Storing Tank Systems:
With these concepts in mind, you can now navigate to the next steps:
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