Rainwater Harvesting 101

Rainwater harvesting is a technique used for collecting, storing and using rainwater for landscape irrigation and other uses. The rainwater is collected from various hard surfaces such as rooftops and/or other manmade aboveground hard surfaces.

This ancient practice is growing in popularity due to interest in reducing the consumption of potable water and the inherent qualities of rainwater.

Below is general information about rainwater harvesting systems, as well as the advantages and disadvantages.

Rain Harvesting 5

Basic Rainwater Harvesting Components

Rainwater systems come in all shapes and sizes, from simple catchment system under a downspout to large above and/or underground cisterns with complex filtration systems that can store thousands of gallons of water.

Most rainwater collection systems are comprised of the same basic components

  • Catchment surface - rooftop or other raised solid surface. The best catchment systems have hard, smooth surfaces such as metal roofs or concrete areas. The amount of water harvested depends on the quantity of rainfall, the size of the surface and the slope of the catchment area.
  • Gutters and downspouts - also known as distribution systems. They channel water from the catchment area to a holding container such as a barrel, cistern or planted area. 
  • Leaf screens - a screen that removes or catches debris.
  • Roof washers - a device that diverts the "first flush" of rain before it enters the storage tank. Most rainwater suppliers recommend that the "first flush" of water is diverted to an outside area of the storage system since the catchment surface may accumulate bird droppings, debris and other pollution.
  • Storage tanks - In general, the storage tank is the most expensive component of a rainwater harvesting system. There are numerous types and styles of storage tanks available. Storage can be aboveground or underground. Storage containers can be made from galvanized steel, wood, concrete, clay, plastic, fiberglass, polyethylene, masonry and more. Examples of aboveground storage include cisterns, barrels, tanks, garbage cans, aboveground swimming pools and more. Storage tank prices vary based on variables such as size, material and complexity. To inhibit the growth of algae, storage tanks should be opaque and preferably placed away from direct sunlight. The tanks should also be placed close to the area of use and supply line to reduce the distance over which the water is delivered. Also consider placing the storage on an elevated area to take advantage of gravity flow. The tank should always be placed on a stable and level area to prevent it from leaning and possibly collapsing.
  • Delivery systems - gravity-fed is the best system.  If you are proposing to use any sort of pump, you must first contact your local water utility.  A rainwater system can never be cross-connected with your potable water system (i.e. the water that supplies your house and irrigation system).  This is because the rainwater could contaminate your drinking water. If a pump is used, it could actually contaminate the water in the water supplier's main line in the street and then contaminate the water in the community.  This is why it is vital to never set up a system that could be cross-connected with your domestic water.

Advantages and Disadvantages of Rainwater Harvesting


  • Makes use of a natural resource and reduces flooding, stormwater runoff, erosion and contamination of surface water with pesticides, sediment, metals and fertilizers.
  • Excellent source of water for landscape irrigation.
  • Home systems can be relatively simple to install and operate.
  • Promotes both water and energy conservation.
  • No filtration system required for landscape irrigation.


  • Because rainfall generally occurs during winter when irrigation is not required, the rainwater needs to be stored until the irrigation season. 
  • Large systems are required if you wish to have an impact on reducing potable water.
  • Can be costly to install. Rainwater storage and delivery systems can cost between $200 to $2,000+ depending on the size and sophistication of the system
  • May not ever be able to “pay for itself” when compared to the low cost of potable water.
  • Requires some technical skills to install and provide regular maintenance
  • CAUTION: If not installed correctly, may attract mosquitoes (i.e.; West Nile Disease and other waterborne illnesses)
  • Certain roof types may seep chemicals, pesticides, and other pollutants into the water that can harm the plants

Safety Considerations

  • Please make sure that children and pets do not climb on the storage systems and accidentally fall into the storage tank.
  • Storage tanks should have locking lids and/or bars that keep the children and pets out!


The following links provide a wide range of information on rainwater catchment.

Rain Barrels and Cisterns

  • A nice summary of how to create a rain catchment system with tips on designing and maintaining.  Provided by Bay Area Storm Water Management Agency Association

Tips to Place and Maintain a Rain Barrel

  • This is a short step by step summary of how to set up a rain barrel system.  Provided by SoCal Water

Saving Rainwater- Not Mosquitos

  • This includes tips so you don’t inadvertently create a breeding ground for mosquitos. Provided by CC Mosquito & Vector Control

American Rainwater Catchment Systems Association

  • This is the national association which has lots of technical information and info for installers

Rainwater Harvesting for Drylands and Beyond

  • This site includes a wide range of information and videos and books.  Provided by Brad Lancaster

Rainwater Harvesting Video

  • This inspiring video describes why we need rain water harvesting and why we need to conserve water. Video is by Brad Lancaster

Basics on installing a Rainwater Harvest System

  • This very good how-to video walks you through the steps to install a system to capture rain water off of your roof. 

Basic Components of a Rainwater Collection System

  • This site provides the basics of installing a rainwater system.  By University of Arizona Cooperative Extension

Rain Harvesting Project

  • The Pleasant Hill Rotary Rain Harvesting Project envisions rain barrels and rain tanks at every residence, business and school in Pleasant Hill! They offer low cost barrels, parts, and installation.