How to Build a Water Cistern

A water cistern is usually a secondary water source used for irrigation or some other specific purpose.

Rain barrel location.Rain barrel location.
Building a water cistern can be an elaborate process or a simple rainwater catchment system. Collecting runoff water from the roof in a rain barrel is a water cistern system. Adding an underground storage tank or a filtration and treatment is a cistern system, but a more complex one.

Clean the roof where runoff will be collected. Be sure there is a large surface area, such as 1,000 square feet of smooth rooftop, to drain into your tank. Clean out any debris from guttering. Pick a site for the tank that allows a space below the spigot to attach a hose or bucket to drain the tank.

Install leaf covers on the guttering. Purchase a precut wire mesh to fit existing gutters. Snap these into place under the lip of the gutter. Fasten them with clips made for this purpose.

Add a runoff system for the first 10 gallons of roof water between the gutter and downspout leading into the tank. Place a downspout in the hole in the guttering made for this purpose. Attach the downspout directed toward the ground. Place an end-cap on the bottom of the downspout. Place a runoff pipe leading to the cistern tank at the top of this downspout. Once the downspout is full, clean water will go to the tank.

Install a cutoff valve that you can open to drain runoff and close to capture runoff. This cutoff valve can be a simple plate that turns to allow water to flow out or hold the water. Set this to drain away from the cistern by placing it perpendicular to the downspout on the side opposite the cistern. Fill it with the first runoff, drain it and close the cutoff valve so water fills this gutter and then goes to the cistern.

Measure the amount of downspout pipes between the gutter and tank. Install downspout from guttering to tank. Install downspout outlet in tank. Cover top of tank with 1/4 inch hardware cloth. Install spigot to release water for use.

Install a second outlet to allow runoff from a full tank to go to a second storage water tank. Place this tank above ground if portable. Place tank underground if you are planning to use a pump system to distribute water.

Things You Will Need

  • Guttering with leaf covers
  • Downspout
  • 1/4 inch hardware cloth
  • Tank or rain barrel
  • Cutoff valve
  • Trickle drain or spigot


  • Locate the cistern near the catchment area.
  • Be sure the roof surface is suitable for this use and will not leach chemicals into the water.
  • Provide thermal cover for freeze protection.


  • If using an underground tank, locate the tank away from possible groundwater contamination by creating a slope above it.
  • Filter or "wash" roof runoff before it enters the cistern to lessen contaminants such as debris and bird droppings.