Cisterns and Rain Barrels

A Rainwater-Collection System Saves Water for Dry Spells

Bird's-Eye View

Using a free resource

Cisterns and rain barrels collect water from the roof and store it for later use. A barrel may be enough for just a small garden, but more elaborate filter and storage systems can provide all the water a family uses. Cisterns can be anything from an old whiskey barrel to an underground concrete tank big enough to store thousands of gallons of water.

See below for:

Key Materials

Getting the junk out of water before storage

Bulk storage of rainwater is a tantalizing idea in areas of the country where groundwater is in short supply. With a large enough cistern, a family could draw on reserves for many months—providing that the water is clean enough.

Commercially available roof washers prevent dirt, leaves and other debris from being swept off the roof and into the cistern. Some washers divert the initial runoff completely before rainwater is allowed into the tank; others use filters. Washing off the roof before rain starts also helps keep water cleaner.

One company that makes roof washers is the Water Filtration Co..

When water is pumped from the storage tank to the house for use, sediment and UV filters are used for final conditioning.

Design Notes

Rainfall patterns are a key consideration

The economics of rainwater catchment have everything to do with climate and storage capacity. If it rains periodically throughout the year, with dry spells in between, you probably won’t need a very large storage tank to see real benefits. On the other hand, if you’re in the western part of the country and get all your rain in just a four-month period, you may want to store much more water for use throughout the dry season.

Because storage tanks and related plumbing can be expensive, deciding whether this is a good investment is very project specific. For more information on rainwater collection, visit Toolbase.

Builder Tips

Water collection systems can be assembled from simple components

There are a number of parts that go into a rainwater harvesting system, but construction is fairly straightforward, and the general components are available from a number of commercial suppliers.

Judging from this account by an Oregon homeowner, the project is entirely feasible for a motivated homeowner. There is regular maintenance involved, however—filters and other parts need to be changed or checked periodically.

The Code

The code

The IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. has little to say about rainwater collection systems, but local code will likely require that all pipes, fittings, and collection vessels be installed according to manufacturers' instructions (section 2608.2) and comply with IRC section 2608.3, which ensures the components meet National Sanitary Foundation standards.


Pay attention to consumption

In regions where enough rain falls during the year to supply a family's needs, a cistern can be a sound investment. Sensible consumption, however, is a key consideration. Low-flow showerheads and faucets, and water-conserving toilets are among equipment choices that can save water. In addition, personal habits may need adjusting. Unnecessarily long showers, or frequently washing the car, can easily undo months of conservation.

In this respect, collecting rainwater is not unlike installing photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. panels on the roof to generate electricity: Hardware is only half the battle.


Standing water in a rain barrel can become a breeding ground for mosquitoes, which may carry disease and are a general nuisance. Rain barrels should be covered, either with a solid top or insect screen, to prevent mosquitoes from moving in.

A cover also will keep leaves and other debris out of the water.


LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. -H: SS4 (Sustainable Sites) offers up to 7 points for on-site stormwater management control. WE1.1 (Water Efficiency): up to 4 points for rainwater harvesting.

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. Under Ch. 5 — Lot Design: up to 17 points for stormwater management (503.4); under Chapter 8 — Water Efficiency: up to 8 points. for rainwater harvesting and reuse (801.11).


Where water is scarce, save the rain

In drought-prone regions, a rainwater-collection system can help stretch scarce water supplies. At its most elaborate, rainwater collection can provide all the water a household uses with no need for backup supplies.

Big rainwater collection systems are expensive. But in a few locations in the American West where competition for water is already fierce, they may be a cost-effective way to furnish domestic water supplies.


Putting a system together

A rainwater collection system designed to supply most of a home's needs would include these components:

Nonporous roof material. Although all roofs shed water, surfaces that have a lot of nooks and crannies are more likely to pick up debris and support the growth of mold, increasing the need for filtering and treatment. A nonporous surface like metal (for example, Galvalume Plus with an acrylic coating) is a much better option.

Gutters and downspouts. Six-inch gutters and five-inch downspouts should be able to handle all the rain that Mother Nature provides.

Cistern. A storage tank of up to 40,000 gallons may be required if a homeowner intends to rely on rainwater exclusively. In-ground concrete tanks are easy to camouflage and don’t need much maintenance.

Filters. Sediment filters and UV filters clean the water once it’s pumped from the cistern to the house, making it suitable for drinking, cooking and bathing.

Image Credits:

  1. Peter L. Pfeiffer/Fine Homebuilding #142
  2. Dan Thornton/Fine Homebuilding #142
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!