A Beginner's Guide to Rainwater Harvesting

Rainwater Harvesting

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Rainwater has been collected, stored and consumed for thousands of years with methods attracting renewed interest today. Modern systems range from rain barrels to elaborate green setups with pumps, piping and filtration elements. Complex installations are best left to professionals knowledgeable about restrictions and permit requirements, but if your goal is a free water source for lawn, garden and other activities, harvesting rainwater is fairly straightforward.


Collecing rainwater for personal use is restricted and even illegal in some states. If you are unsure about restrictions in your state, contact your local cooperative extension office for information.

Benefits of Harvesting Rainwater

Rainwater is useful in a myriad of ways with advantages over water out of the tap from municipal systems.

  • Conservation: In many parts of the world, water is a limited resource with demand greater than supply. Using rainwater helps protect and conserve natural resources like rivers and streams and reduces demand on public utilities.
  • Cost: Rainwater is free. Complex and potable systems require some investment, but the bottom line for the average homeowner is a lower utility bill.
  • Neutral pH: Rainwater is soft with a neutral pH which makes it ideal for personal hygiene, laundry, and cleaning. It's less corrosive than hard water and can extend the life of appliances.
  • Contaminant free: Man-made chemicals and pollutants are not present in rainwater, which is better for plants. Unlike municipal systems, it's free from disinfection by-products, salts, minerals, and contaminants.
  • Reduces stormwater runoff: Collection and storage mean less water funneled into storm drains, which also reduces flooding and the spread of groundwater pollutants.

Techniques for Harvesting Rainwater

There are basically two techniques for rainwater collection: surface runoff and groundwater recharge. Both techniques include some or all of these parts:

  1. Catchment surface: the surface where rainwater collects
  2. Gutters and downspouts: conduits for channeling water
  3. Diverters and roof washers: remove dust and debris
  4. Storage tank: rain barrel, cistern or reservoir
  5. Delivery system: gravity fed or pumped to end location
  6. Treatment: filters and other equipment to make the water potable.

Surface Runoff Harvesting

Surface runoff collection directs rainwater from a flat surface through a conduit into a storage container. This technique is fairly simple and a good starting point for homeowners who want to harvest rainwater for home and outdoor uses, such as watering indoor and outdoor plants, cleaning. and personal hygiene.

The method most familiar is rooftop runoff. A catch basin such as a rain barrel is placed under a building downspout to collect and store rainwater.

Surface runoff is also practical for rain gardens or any garden bed where a gutter can direct surface runoff into the designated area.

Groundwater Recharge

Groundwater recharge is a system built to collect rainwater runoff at ground level. It's more complex and requires initial construction costs for a storage tank (usually a cistern or reservoir), a pump, and distribution elements including piping.

The catch basin is positioned at the bottom of a downhill slope to capture excess rainwater that saturates the ground. You can use dipping buckets for retrieval, but more often a pump is installed for retrieval and distribution. Moving the water for irrigation or household plumbing requires piping.

Recharge has more applications for use such as crop irrigation, managing livestock, and even supplying water for household plumbing.

Types of Rainwater Collection

Types of rainwater harvesting are largely determined by the storage and distribution equipment needed. Collecting rainwater for personal use can be as simple as setting out a bucket.

Rain Barrels

The rain barrel serves as the catch basin. Most commercial types are constructed with molded plastics, but a large garbage can works too. The barrel requires a tight-fitting lld with the center cut out and replaced with a small mesh screen to filter out leaves and other debris. A spigot with an on-off valve is installed on the lower portion of the barrel.

Rain barrels are usually placed directly under a gutter or downspout. The lid can be removed and water dipped out for use, but a spigot offers easier access with less effort on your part. The higher the spigot is placed, the greater the water pressure on release. Keep in mind, though, that it won't equal the pressure supplied by a municipal water source.

Rain barrels should be cleaned or flushed annually. Some commercial barrels are made to withstand freezing temperatures. You can also insulate or move yours to an indoor location in colder climates.


Rain barrels are a fairly simple DIY project and available for purchase at retail outlets and garden centers. Some local governments and conservation organizations offer free barrels as incentive for homeowners.


Cisterns are underground or partially submerged, covered structures that hold and pump out water. Built with cinderblocks, cement, steel, or fiberglass, they are most efficient located on the downside of a slope or, in the case of household systems, close to the foundation at its lowest level.

During rainfall, surface groundwater is directed into the cistern, "recharging" the storage tank with fresh water. Pumps powered by electricity or solar energy retrieve the water. Piping may be included for distribution. Depending on the type of pump, water can be directed to areas distant from the source.

A cistern does require upkeep including regular cleaning of both the storage unit and distribution system. Piping may also require insulation or winterizing in colder climates.

Choosing the Right Method

There are lots of rainwater harvesting options available, so before deciding which way to go, here are a few considerations.

  1. The average rainfall amount in your location.
  2. How you plan to use it.
  3. How much water you need.
  4. How long you need to store it.

Remember to factor in filtration and purification costs if your end goal is potable water or a more elaborate system with large storage capacity.

  • Is rainwater drinkable?

    Harvested rainwater is not considered potable. However, the addition of a filtering system can make it suitable for drinking and cooking. Some type of purification element is recommended to remove bacteria collected from surfaces like roofs.

  • Can you install your own rainwater harvesting system?

    Yes. The simplest place to start is with a rain barrel. The more complicated the system, the greater the need for design, engineering, and plumbing expertise.

  • What's the difference between a reservoir and a cistern?

    A reservoir is often a natural depression formed by rock, but can be built with materials used for cisterns. Reservoirs are uncovered and open to the elements.

Article Sources
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  1.  Saving and Using Rainwater . UF/IFAS Extension.

  2. Rainwater collection. The Centers for Disease Control and Prevention