Water-Efficient Technology Opportunity: Rainwater Harvesting Systems (2022)

The Federal Energy Management Program (FEMP) identified rainwater harvesting systems as an alternative water technology that is relevant to federal facilities, is commercially available, and may offer an opportunity to offset freshwater use. This technology overview is intended to provide agencies with key information to deploy rainwater harvesting systems.

Technology Description

Harvested rainwater can provide a source of alternative water to federal facilities. Alternative waters are sustainable sources of water, not supplied from fresh surface water or groundwater, that offset the demand for freshwater. Rainwater harvesting captures, diverts, and stores rainwater from rooftops for later use. Typical uses of rainwater include landscape irrigation, wash applications, ornamental pond and fountain filling, cooling tower make-up water, and toilet and urinal flushing. With additional filtration and disinfection, harvested rainwater can also be treated to potable standardsto supplement municipal potable water supplies to facilities.

System Components

The major components of a rainwater harvesting system are displayed in Figure 1.

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  1. Collection system: Roof surface and gutters to capture the rainwater and send it to the storage system
  2. Inlet filter: Screen filter to catch large debris
  3. First flush diverter: Diverter that removes debris not captured by the inlet filter from the initial stream of rainwater
  4. Storage tank: Storage tanks composed offood-grade polyester resin material approved by theU.S.Food and Drug Administration (FDA), which is green in color and helps to reduce bacterial growth
  5. Overflow: Drainage spout that allows for overflow if the storage tank gets full
  6. Controls: Control system that monitors water level and filtration system
  7. Treatment system: Filtration and disinfection system that treats the water to non-potable or potable standards
  8. Pump: Pump to move water through the system to where it will be used
  9. Backflow prevention: Backflow preventer to ensure that under negative pressure water cannot flow backwards through the system into the make-up water system
  10. Flow meter: Flow meter (with data logger) to measure water production
  11. Power supply: Systems may use either conventional power sources or, to improve off-grid capabilities, alternative sources such as stand-alone or grid-tied solar systems
  12. Water level indicator: Monitors the water level in the storage tank

Technology Considerations

The following are important considerations when planning for a rainwater harvesting project.

  • End Use: The intended end use of the harvested rainwater will determine the type of treatment equipment that the system will need.
  • Site location: Choose sites with adequate rainfall for the application. For more information, see the Rainwater Availability Map.
  • Applications: Choose a location that has multiple applications that can use rainwater, such as vehicle wash, landscape irrigation, and dust suppression.
  • Size of catchment area (roof size): A larger roof area can capture significant amounts of precipitation, even in areas of low rainfall availability.
  • Rainwater storage capacity: Areas with less frequent precipitation may require larger tanks to provide more storage capacity between water recharge. Anincreased tank size will increase equipment cost.
  • Roof pitch and type: Roof material and pitch influence the amount of water that can be harvested. Lower-pitched roofs tend to catch more water than steeply pitched roofs. Smoother roof textures will facilitate runoff better than textured roofs.
  • Water rates: Areas with higher water rates will make rainwater harvesting projects more economically viable.
  • Permits: Rainwater harvesting permits may be required. Check with your local or state government. For more information, see the Rainwater Harvesting Regulations Map.

System Sizing

Here are the basic steps to properly sizing the storage tank of a rainwater harvesting system.

  1. Determine how much rainwater is available for harvesting. FEMP'sRainwater Harvesting Toolcan be used to estimate the amount of monthly rainfall over a typical year that can be collected from a rooftop or other hard surfaces.
  2. Estimate the application’s water demand over the same period. If possible, determine the monthly demand for the application over a full year.
  3. Compare the amount of monthly rainfall that can be harvested to the monthly water demand over the year. Is there generally enough rainfall to supply a significant portion of the application’s demand?
  4. Determine an optimal storage tank size that provides enough volume to store adequate rainfall to meet the demand while not oversizing the tank.

Note: If there are large variations in rainfall throughout the year, a larger tank may be necessary to store rainwater during wet months for use during drier months. Additional treatment may be necessary to maintain water quality. In addition, it may be advantageous to compare weekly precipitation to weekly demand to get a more precise picture of the availability of rainfall to meet the water requirements of the application.

FEMP's Rainwater Harvesting Tool uses the following formula to calculate the monthly rainwater available for harvest:

Monthly Rainfall Collected (gal)

= Catchment Area (roof size)(square feet) × Monthly Rainfall (inches)

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× Conversion Factor × Collection Factor


  • Catchment area (roof size) is the size of the roof where rainfall will be collected
  • Monthly rainfall is total amount of rainfall (in inches) for the month
  • Collection factor is a factor applied to the total monthly harvesting potential to account for losses in the system. The Texas Manual on Rainwater Harvesting recommends using between 75% and 90%, depending on how efficiently the rainwater harvesting system collects rainfall
  • Conversion factor is a factor of 0.62 used to convert the total amount of rain (in inches) that falls onto the roof area to total monthly gallons of harvesting potential.

Operation and Maintenance

Rainwater harvesting systems require regular operation and maintenance. Generally, the components of the system are made to last with regular upkeep, and manufacturers will often provide several years of warranty, anywhere from 15 to 30 years for storage tanks and pipework, and typically twoto 10 years for pumps.

Table 1 lists the recommended operations and maintenance (O&M)actions for the major components. These actions should accompany actions recommended in manufacturer materials specific to the installed equipment.

Table 1. Rainwater Harvesting Components Shown in Figure 1 and Associated Maintenance Actions

NumberComponentDescriptionMaintenance ActionsSuggested Frequency
1Collection systemRoof surface and gutters to capture rainwater and send it to the storage system.

Keep clean and clear of excessive debris, especially after prolonged dry periods or after storms.

Inspect roof surface and ensure water flows and drains properly as intended.

2Inlet filterScreen filter to catch large debris.Clean out filter and replace at regular manufacturer-specified intervals.Weekly; manufacturer-specified intervals
3First flush diverterDiverter that removes debris not captured by the inlet filter from the initial stream of rainwater.

Keep clean and clear of excessive debris, especially after prolonged dry periods or after storms.

Ensure the diverter is functioning as intended, diverting only the initial flush of water during rainfall.

Monthly and after prolonged storms
4Storage tankStorage tanks composed of FDA-approved, food-grade polyester resin material that is green in color, which helps to reduce bacterial growth.

Inspect tank for cracks or leakage.

Infrequent blowdown may be needed to remove sediment from the bottom of the tank. If filters are regularly maintained, sediment accrual should be minimal (2 mm to 2 in. per year).

5OverflowDrainage spout that allows for overflow if the storage tank gets full.

Visually inspect overflow spout to ensure it is clear of debris.

6ControlsControl system that monitors water level and filtration system.

Ensure controls operate as intended, visually confirm response to control commands. Request manufacturer maintenance as needed to repair any controls issues.

Check that wiring is in good condition.

7Treatment systemFiltration and disinfection system that treats the water to non-potable or potable standards.

Clean and replace filters at manufacturer-specified intervals.

Ensure treatment system dosing intervals are sufficient to meet water quality requirements in the system.

Manufacturer-specified intervals
8PumpPumps move water through the system and to the end use.

Check motor condition. Investigate excessive vibration, noise, or temperature.

Perform pump maintenance, such as bearing lubrication, in accordance with manufacturer specifications.

Monthly; Manufacturer-specified intervals
9Backflow preventionBackflow preventer to ensure that water cannot flow under instances of negative pressure.

Have an approved professional test annually or at a frequency required by local regulation.

10Flow meterFlow meter (with data logger) to measure water production.

Ensure meter is calibrated per meter manufacturer instructions.

Track water use regularly through meter readings automatically (with data logger) or manually with a log book.

11Power supplySystems may use conventional power sources, or, to improve off-grid capabilities, may use alternative sources such as stand-alone or grid-tied solar systems.

Check power supply and equipment after power outages and ensure no damage to components.

Follow manufacturer operation and maintenance guidelines for alternative stand-alone power supplies (e.g., solar photovoltaic panels).

As needed; Manufacturer-specified intervals
12Water level indicatorMonitors the water level in the storage tank.

Ensure the indicator is functioning as intended.

13 (not shown in Figure 1)Potable water connectionMake-up water supply (e.g., municipal water) to meet system needs when rainfall is not adequate to meet demand (not pictured).

Inspect potable water supply connection and backflow preventer and ensure that connections are in good condition without leaks.

Comply with any regulations for testing required by local ordinances.


Treatment for Potable Application

Harvested rainwater is typically used in non-potable applicationsbut can meet potable standards with additional treatment. For potable systems, a licensed operator must maintain the system to ensure that it continues to produce water at a quality fit for human consumption. Additional considerations and components more specific to potable systems are shown in Table 2.

Table 2. Additional O&M considerations specific to a potable rainwater harvesting system

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ComponentDescriptionMaintenance ActionsSuggested Frequency
Water qualityWater must be regularly tested by a licensed operator to ensure it is safe for human consumption.

Perform water quality test; check water quality for proper chemical balance.

Monitor turbidity level.

Test pH, temperature, and disinfectant residual.

Filter cartridges/membranesWater is pumped through the filters/membranes that must remove at least 99% of particles that are 3.0 microns or larger in diameter. This is sometimes achieved in stages with filters set up in series.

Replace filters as needed per manufacturer recommendation.

Manufacturer-specified intervals
Disinfection systems – May be a combination of ozone, chlorination, and ultraviolet (UV) radiationDisinfection systems are capable of inactivating (or killing) viruses that might be in the water.

Ensure dosing intervals are set as needed to sufficiently disinfect the amount of water processed through the system. Ongoing monitoring is essential to achieving this requirement.

Ensure chemical supply and injection system levels are adequate.

Replace equipment such as ultraviolet (UV)lights at the end of their life. A UV lamp typically lasts about onyear, and its effectiveness begins to diminish as it ages.

Ceramic and titanium plates, fuses, and filters in ozone generators may need to be cleaned or replaced. Consult manufacturer specifications for frequency of maintenance.

Daily; Manufacturer-specified intervals

Related Links

FEMP created a series of alternative water maps to help federal agencies strategically plan where to implement alternative water projects. Three of these maps and one tool cover rainwater harvesting:

  • Rainwater harvesting regulations: State-by-state listing of rainwater harvesting regulations
  • Rainwater harvesting: Tool that estimates the amount of monthly rainfall that can be harvested from rooftops or other hard surfaces
  • Rainwater availability: Range of available rainwater for harvesting across the U.S.
  • Rainwater availability for landscape irrigation: Range of available rainwater across the U.S. to supplement irrigation requirements of traditional landscaping.

More Opportunities

Read about these additional water-efficient technology opportunities.

  • Distribution System Leak Detection
  • Advanced Cooling Tower Controls
  • Connectionless Food Steamers
  • Multi-Stream Rotational Sprinkler Heads
  • On-site Wastewater Treatment Systems
  • Sprinkler Automatic Shut-Off Devices
  • Steam Sterilizer Condensate Retrofit Kit
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What are technologies in rainwater harvesting? ›

Usually, there are two basic ways of rainwater harvesting like surface runoff harvesting and rooftop rainwater harvesting. In the first method, rainwater flowing along the surface is collected in an underground tank. In the second method, rainwater is collected from roof catchment and stored in a tank.

What are the two main techniques of rainwater harvesting answer? ›

Surface runoff harvesting and groundwater recharge are the two primary techniques of rainwater harvesting.

What benefits will we get from rain water harvesting? ›

It reduces soil erosion, stormwater runoff, flooding, and pollution of surface water with fertilizers, pesticides, metals and other sediments. It is an excellent source of water for landscape irrigation with no chemicals, dissolved salts and free from all minerals.

What is the main purpose of a rainwater system? ›

Rainwater Harvesting is the collection and storage of rainwater that would otherwise flow down gutters into the drain. Rainwater is collected from the roof, then re-used within the home and garden. This can provide substantial savings on water bills, as well as making your home more sustainable.

What is the importance of water harvesting in agriculture? ›

Instead of runoff being left to cause erosion, it is harvested and utilized. In the semi-arid drought-prone areas where it is already practised, water harvesting is a directly productive form of soil and water conservation. Both yields and reliability of production can be significantly improved with this method.

Why water harvesting is important for agriculture? ›

WH enables farmers to store water when it is plentiful and make it available when it is scarce. Three categories of small-scale storage can be distinguished: 1) soil moisture storage; 2) groundwater storage; and 3) surface storage.

What are three ways to maintain a rainwater harvesting system? ›

Wash off roof with water when dust/dirt accumulates diverting runoff way from tank inlet. Monthly and especially after a long period of dry weather or heavy wind. Fix damage to roof (broken tiles, cracked water-proofing etc.)

What is the conclusion of rainwater harvesting? ›

Rainwater harvesting improves water supply throughout the year; with fluctuating climate change and the elimination of groundwater storage, rainwater harvesting helps mitigate those effects. This can help recharge groundwater storage and ensure water availability in scarce areas.

Is rain water harvesting good for the environment? ›

Rainwater harvesting helps manage stormwater runoff to prevent erosion, flooding, and poor water quality in our lakes and streams.

How much water can rainwater harvesting save? ›

Rainwater replaces, on average, around 40-50% of your mains water usage, so a property owner can realistically expect to make a saving of around 45% on their water bills.

How is rain good for the environment? ›

Precipitation supplies the water that terrestrial organisms need -- either directly in the form of rain that falls on soil where plants grow, or indirectly in the form of lakes, streams and ponds where animals can drink.

How does water harvesting work? ›

Rainwater is captured through the drain pipes on a building's roofs or elsewhere. The stored rainwater is then passes through a filter to make it clean for consumption. The harvested rainwater can be stored in a single or multiple tanks that are connected, either under or above the ground.

What is rainwater harvesting very short answer? ›

Rain water harvesting is collection and storage of rain water that runs off from roof tops, parks, roads, open grounds, etc. This water run off can be either stored or recharged into the ground water.

How can we save rainwater essay? ›

Here, the roof of a house or building works as a rainwater collection unit. It includes equipping the roof with pipes that direct to a pit or tank. These pipes will divert the water falling on the roof in the tank to save water from falling off. This is a very economical and efficient way to harvest rainwater.

How long can you preserve rain water? ›

You probably know the benefits of using rainwater for plants, but how long can you keep it and use it on your plants? Generally, rainwater will become contaminated after about one week. You can prolong its lifetime indefinitely by keeping it out of the light and from animal and insect contact.

How can we reuse rain water? ›

Uses. Harvested rainwater can be safely used for non-potable activities, such as yard and landscape irrigation, watering potted plants and washing vehicles. Collected rainwater should NOT be used for drinking or other potable purposes if it is not filtered and disinfected before use.

How do you collect rain water at home? ›

Rain Barrels – This is the simplest and most affordable way to harvest rainwater. You simply place barrels or water tanks below the downspouts of your gutter system. This tank can be connected to a pipe for drip irrigation. Dry System – A dry system uses a larger storage container for the water.

What is the observation of rain water harvesting? ›

Rainwater harvesting from roof is considered as valuable water resources. Material Flow Analysis (MFA) of water in Mahasarakham University (Khamriang Campus) shows that rainwater harvesting from roof can reduce water supply production by 7% and save more than 200,000 Bt/year for water treatment cost.

What are the different techniques of water harvesting? ›

Qanat systems, underground dams and special types of wells are a few examples of the groundwater harvesting techniques. Groundwater dams like 'Subsurface Dams' and 'Sand Storage Dams' are other fine examples of groundwater harvesting.

Is rainwater harvesting green technology? ›

Rainwater harvesting (RWH) is the most traditional and sustainable method, which could be easily used for potable and nonpotable purposes both in residential and commercial buildings. This could reduce the pressure on processed supply water which enhances the green living.

What are the different types of rainwater harvesting? ›

There are three main types of rainwater harvesting system: direct pumped, indirect pumped, and indirect gravity.

Which is the best method of water harvesting? ›

Use rainwater effectively.

Storage techniques (such as external catchments or roof top collection) increase the availability of water in the drier seasons. They also harvest water from a wider area making more water available to the crop.

What is the conclusion of rainwater harvesting? ›

Rainwater harvesting improves water supply throughout the year; with fluctuating climate change and the elimination of groundwater storage, rainwater harvesting helps mitigate those effects. This can help recharge groundwater storage and ensure water availability in scarce areas.

Is rainwater harvesting good for the environment? ›

Rainwater harvesting helps manage stormwater runoff to prevent erosion, flooding, and poor water quality in our lakes and streams.

Is rain water safe to drink? ›

You may even rely on bottled water to meet your daily water needs. But what about rainwater — is it a safe and healthy source of drinking water? Rainwater that falls from the sky is typically free from contaminants, and should by all accounts be perfectly safe to drink.

Why is rain good for the environment? ›

Precipitation supplies the water that terrestrial organisms need -- either directly in the form of rain that falls on soil where plants grow, or indirectly in the form of lakes, streams and ponds where animals can drink.

How many water harvesting methods are there? ›

Broadly there are two ways of harvesting rainwater, namely; surface runoff harvesting and rooftop rainwater harvesting.

What is the importance of water conservation? ›

Conserving water saves energy. Energy is needed to filter, heat and pump water to your home, so reducing your water use also reduces your carbon footprint. Using less water keeps more in our ecosystems and helps to keep wetland habitats topped up for animals like otters, water voles, herons and fish.

How we can conserve water? ›

Do not let the water run while shaving or brushing teeth. Take short showers instead of tub baths. Turn off the water flow while soaping or shampooing. If you must use a tub, close the drain before turning on the water and fill the tub only half full.

Why is water storage important? ›

The purpose of water storage tanks is usually to maintain water service pressure, maintain emergency storage supply and pressure during power outages, and provide equalization volume to meet peak demands, such as fire flows and times of the day when water use is high.


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