Residential Storm Water Practices

Capturing Runoff for reuse

Why install a cistern?

Cistern under deckCisterns (big rain barrels that hold 200-1000 gallons or more) can help reduce the peak storm runoff that damages our streams and causes sewer overflows. They can also hold water to irrigate your lawn and garden in summer. To get both those benefits, you need to leave the drain valve open during the winter so that heavy rains and snow can fill the cistern and then slowly drain out (before the next storm). Then, you can close the drain during growing season so your cistern fills to store water for irrigation. Open the drain again before winter – it's that easy!

Is a cistern right for me?

CisternIf you are good with tools, or can afford to hire a contractor, there are cisterns (or multiple smaller cistern/barrel systems) that can fit most yards.

You need:

  • A level location near a downspout, outside (not inside a building)
  • A solid base (packed earth or sand, concrete, etc.)
  • To allow enough space for ingress and egress: A safe place to discharge the overflow(after cistern fills) a minimum of:
    • 5 feet from any structures on crawl-space or slab foundations
    • 10 feet from any structures with a basement, plus 2 feet more for each foot the basement extends below 5 feet deep.
    • You may not discharge overflow onto neighboring properties.

Getting started – planning and shopping

You'll need to plan carefully, and shop around for your cistern tank, other materials, and a contractor (if needed). See the NebraskaH2O and UNL Extension (under "Water Management") websites for help.

  • Start by talking to your neighbors, if it will be visible to them. A low fence or trellis can help improve appearance.
  • Shop around for cistern tanks. While reused tanks may be available, the safest choice is a new tank. The cheapest source may be agricultural suppliers, since farmers already use plastic tanks for many needs. Choose a dark-colored tank to limit algae growth, and place in a shaded location.
  • Decide whether to go above ground or below. (Below-ground tanks are more expensive and harder to install and may require pumping)
  • Decide on a location, and foundation. A full tank is heavy (water weighs 8.4 lb./gallon) – you need a level, firm foundation to hold one safely. Tanks that are higher than they are wide typically need to be secured for wind protection, so it's easier to use shorter, wider tank. A shaded location (on north side of house) will limit algae growth.
  • Shop for pipe and connectors (ABS or PVC Schedule 40 plastic is best) to connect your downspout to a screened inlet, to your tank, to an overflow, and to a drain valve (a garden-hose faucet works well).
  • Hire a contractor or engineer to plan or install, if this sounds like too much.

How to Install a Cistern

  1. Diagram for installing a cisternLevel the ground (use a carpenter's level) and pack the soil hard.
  2. Build a level foundation. Place 4-6 inches of packed sand, or concrete pavers, or poured concrete, over packed subsoil. Your cistern tank supplier should provide specifications.
  3. Place the tank – check that it's level, sitting on smooth sand, gravel or concrete. Follow the tank supplier's directions.
  4. Secure the tank for wind safety, if it's taller than it is wide, to a building or frame. Follow the supplier's directions.
  5. Install a screened inlet to keep debris (and mosquitoes) out of the tank. An aluminum window screen over the tank inlet works. Adding a self-cleaning downspout screen or gutter filter above it will keep leaves from clogging the inlet screen. Google "Downspout Filters, Screens" on the internet, or ask at your hardware store. For more elaborate systems, Google "First Flush Diverters, Roof Washers, or Cistern Installation" or check local plumbing and drainage suppliers.
  6. Make gutter connections so that roof runoff waterfalls into the screened inlet.
  7. Install a 3-4 inch diameter overflow pipe so that rapid flows from big storms can overflow safely after the tank fills. Place a "P" trap (optional) somewhere in the overflow, to keep mosquitoes and rodents out.
  8. Extend the overflow pipe to a safe discharge point, where water can spread out into a lawn or landscape area. See "discharge distances" recommended above.
  9. Install a drain valve, usually a garden-hose faucet. Connect a garden hose to the faucet.Like the overflow pipe, run the garden hosefrom the drain to a safe place for water tosoak into the soil or flow to the street drain.

Using your cistern

During the rainy season, leave the drain faucet open, or partly open, so the cistern can slowly drain out through the hose between storms. That way, when a big storm comes, it's ready to hold and slowly release the excess flow from your roof. That helps reduce flooding, sewer overflows, and erosion in our streams. In mid-May, close the faucet valve so your cistern fills up to store water for summer. Use your cistern to catch rainwater for irrigation or other outdoor uses all summer. Then open the valve again after the growing season, to help protect our streams all winter.

Disclaimer: This page contains general principles only, which may not be appropriate or safe for every property or project. Use good common sense. You assume the risk and are responsible for all consequences of your modifications to drainage flow or your property, for legal compliance, and for necessary permits and authorizations. The City of Columbus is not responsible for your modifications and disclaims liability for your actions.

Draining Swimming Pools
Because swimming pools are sanitized with chemicals, the water may not be appropriate for direct release as storm water. Water that has recently been chemically sanitized by chlorine will be above the EPA limit for stormwater discharge into the storm sewer system. If immediate discharge is necessary, emptying into the soil is recommended. The soil will safely filter out most of the residuals and sediments. The following requirements must be followed in order to discharge into the storm sewer:

  • The residual chlorine does not exceed 0.1 mg/l (parts per million);
  • The pH is between 6.5 and 8.5;
  • The water is free of any unusual coloration;
  • There is no discharge of filter media;
  • There is no discharge of acid cleaning wastes;
  • The discharge will not cause erosion; and
  • The discharge will not cause transport of pollutants such as: motor oil; pet waste; trash and other debris into the storm drain system.