Rainwater Harvesting

What is Rainwater Harvesting?

Rainwater Harvesting is the collection, storage, and reuse of Rainwater for domestic or agricultural use. In California, rainwater may be collected from rooftops or other aboveground hard structures.


TCRCD's Rainwater Harvesting Rebate Program Information:

Rebate Program Guidelines

Rainwater Catchment System Rebate Application

Rainwater Catchment Rebate Flyer

Rainwater Harvesting Do's and Don'ts:

  • Make a Plan for your rainwater reuse: Storage is great but having a plan to use your water is better.
  • Size rainwater tank to expected water catchment off roof or structure. Follow this link to help size your tank. http://rainwaterharvesting.tamu.edu/calculators/
  • Have a good placement plan in mind for your tank.  Do you want to have gravity fed rainwater or do you need to pump it? How does your roof height compare to your tank height? Remember. if your roof height is lower than the top of your tank, that level will be your tank filling limit.
  •  Create a solid pad for your tank. Water is pretty heavy, roughly 8 lbs per gallon.  So if you have a 1,000 gallon tank, you need to support 8,000 lbs plus the weight of your tank,  A flat gravel pad, graded and compacted, will usually do the trick.
  • Filter your water. Use a pre-filter (a First Flush Device or similar) to separate large debris from your water before it gets to the raintank. The level of post-filtration will depend on your final water use.  A mechanical filter (such as a 200 micron screen filter) is a minimum, if you want to be able to drink your water, post-filtration gets a bit more involved.
  • Never fully close your tank. All water tanks, not just rainwater, should be vented to prevent tank rupture. This opening should be screened to prevent mosquitoes and other critters from getting into your water supply.
  • Install a tank overflow. Once your tank is full, any extra rainwater will need a place to go. Your overflow piping outlet should be placed slightly lower in height on the tank than the inflow piping. The overflow pipe should be the same size, or larger than, the inflow piping. Lastly, have a plan for where the this extra water will go. A rain garden is generally a good choice but any measure that reduces erosion and prevents flooding will work.
  • If you live in a seismic zone, or you have a tank taller than it is wide, do tie down your tank. Anchoring down your tank will prevent tipping and protect you and your home.
  • Remember to incorporate other water saving measures too.  Leak detection and installing low-flow irrigation may not sound exciting but many times those two measures will save a person more water than they can easily catch off their roofs.


Best Rain Tank Uses   . . .  Here are a few uses for your rainwater storage:

  • Outdoor irrigation
  • Toilet Flushing: with proper treatment and disinfection rainwater can used for flushing
  • Laundry Usage
  • Water Gardening or Water Feature make-up water
  • Car Washing
  • Fire Protection
  • Other Domestic Non-Potable uses
  • Long Term Storage
  • Resilience: stored water can be a great resource in times of natural disaster or serious need



Rain Tank Example Plans

How to Size Your Tank:

1.     Your tank size is dependent on your needs, your annual average rainfall, and your available space. Follow this link to a rainfall calculator which will help you choose which tank size is right for you.

(Link to Texas A&M Tank Balance)


2. Brad Lancaster's Rainwater Harvesting Calculator



  • Not opaque. Stored water needs to be protected from the sun to prevent algae growth
  • Lighter color keeps water cooler
  • Potable plastic is needed if using water for drinking
  • Non-galvanized if used for irrigation (or use liner)
  • Underground tanks should have swivel unions and flexible line
  • Covered, but accessible
  • Seismic requirements for larger tanks, especially vertical



Example 2,800 Gallon Rain Tank

Why Not to Use a Rain Barrel:

Rain barrels can be a great introduction to water harvesting. They're light, easy to plumb, generally hold about 50 galllons, and seem to have a low initial cost. However, especially in California's dry climate, 50 gallons of water storage is quickly seen to be just a drop in the bucket.  'Daisy-Chaining' or plumbing extra tanks onto your first tank can increase your water storage but as more are added, your cost and maintenance problems increase too. A better solution is to work out your water needs, do a water audit, before you buy any storage items.  Determine your storage needs first and you will only need to buy and plumb one vessel.  In the long run this approach will save you time, money, and headaches.

Tanking Siting Considerations:

Here are a few considerations to take into account when deciding where to place your rain tank:

  • Gravity: If you want gravity flow from your tank, you will need to find the highest possible elevation location for your tank.
  • Electrical: If you are going to pump your water, try to place tank near an electrical source and leave room for filtration piping.
  • Infiltration: your overflow water will need somewhere to go. Ideally, your surrounding soils can accept the water.
  • Aesthetics: tanks are a beautiful thing but they can obstruct a view.
  • Slope: Remember a full tank is a heavy tank, if placed on too steep of a slope, you run a greater risk of your tank tipping.
  • Heat: Choose a spot that is shaded and protected from anything that might damage the pipes (children, cows,horses etc….)
  • Distance: The closer you place a take to rain gutters the less money and materials you'll need to get it piped.
  • Design Your Overflow! think about where your water is going and install an appropriate measure - Rain garden, swales…etc.
  • Do not place tank on top of utility lines (call before you dig)


Low Legacy Wall Rain Pad



Permitting Information:

Calaveras Building Permit website:  http://building.calaverasgov.us/

Tuolumne Building Permit website: http://www.tuolumnecounty.ca.gov/index.aspx?NID=171

Professional Help:

Sierra Watershed Progressive www.sierrawatershedprogressive.com

Laura Allen http://greywateraction.org/

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