What is Rainwater Harvesting?

Dec. 1, 2022
Discussing the process of rainwater harvesting, including how it works, its costs, uses, benefits, and setbacks.

Rainwater harvesting is a penny-saving way to store and access water directly from nature. 

This article will discuss the process of rainwater harvesting, including how it works, its costs, uses, benefits, and setbacks.

What Is Rainwater Harvesting?

Rainwater harvesting is a type of water recycling that involves collecting rainwater for a variety of uses. The water is usually filtered and stored in a holding tank before use. 

The purpose of rainwater harvesting is to reduce the costs associated with receiving treated municipal water. Rainwater can be used both as a primary water source and an emergency backup water supply.

How Does Rainwater Harvesting Work?

Rainwater harvesting works by catching rainfall or directing rainfall into a collection tank from a roof or a similar surface. 

The rainwater is filtered as it travels into the tank to remove large debris (such as leaves and insects), before being pumped into the home or manually collected for use. 

Most rainwater systems end with a thorough filtration process to ensure water is safe for drinking. 

Elements Used In A Rainwater Harvesting System

The elements usually found in a rainwater harvesting system are: 

Pre-Tank Filter

As water flows into the tank, it is filtered by a pre-tank filter, which prevents debris such as leaves and dirt from entering. 

Water Storage Tank

A water storage tank stores the rainwater before use. The tank’s size and capacity depends on its intended use and the available space. Some tanks are buried underground, while others are placed above ground at the side of a building. In domestic properties, the tank is fed from an overhead gutter on the building. 

Control Unit

To monitor the holding tank’s water level, a control unit is used. Some control units offer insight into the water pressure and temperature, and some can even detect faults in the system.

Water Pump

Underground storage tanks need a pump, which sends water up to ground level for use. 

Separate Pipe System

Because rainwater is usually contaminated, and isn’t a consistently reliable water supply, many states require separate pipe systems to be used for rainwater harvesting. This pipe system should connect to appliances that will use the harvested rainwater, including toilets, showers and washing machines.

Water Filtration System

Rainwater is generally non-potable and unsuitable for drinking when it is collected. To make water safe to drink, a multi-stage water filtration system can be built into the separate pipe system.  

Uses of Harvested Rainwater

There are numerous possible uses of harvested rainwater: 

For Drinking

Properly treated harvested rainwater can be used for drinking. As long as the water is filtered by a system that removes particles as small as 5 microns, and purified with technology that kills bacteria and other pathogens (such as UV treatment), rainwater is safe and suitable for drinking. 

Shower Water

Treated rainwater can also be used to supply showers and baths. A rainwater harvesting system can be connected directly to a shower or bath, or to a dedicated water heater to warm the water before use. 

In Toilets

One of the easiest uses of harvested rainwater is in toilets. Since it is not necessary for toilet water to be potable, rainwater does not need to be treated with filtration if its sole use will be to flush toilets. The rainwater is pumped to the cistern through dedicated pipes.

For Gardening & Irrigation

Harvested rainwater can also be used for gardening and irrigation purposes. Using rainwater to grow plants and crops in large-scale applications can save thousands of dollars per year. Rainwater doesn’t need to be filtered for this purpose. 


Some farmers choose to use harvested rainwater as a drinking water supply for livestock, cutting down on the expense of using normal tap water. 

Rainwater Harvesting System Cost

The cost of a complete rainwater harvesting system is $4,000-$15,000, depending on the size and complexity of the system. 

Residential rainwater harvesting systems cost about $2,500. Homeowners can pay as little as $120 for a basic system involving a small, single barrel. 

Benefits & Setbacks of Rainwater Harvesting

Rainwater Harvesting Benefits 

  • Reduces water bills - Households that can harvest enough rainwater for everyday use can enjoy greatly reduced water bills. 
  • Numerous uses - Harvested rainwater has a host of uses, from irrigation and showering to toilet flushing and drinking (as long as it is properly filtered).
  • Reduces groundwater demand - The demand for groundwater (a limited below-ground supply of water) is increasing, and harvesting rainwater reduces this demand and conserves groundwater until it is needed. 
  • Reduces flood risk and soil erosion - Large-scale rainwater harvesting reduces surface runoff, decreasing soil erosion and the risk of flooding. 

Rainwater Harvesting Setbacks

  • Expensive to set up - Installing a complete rainwater harvesting system costs thousands of dollars. 
  • Water filtration required - Most states require collected rainwater to be filtered to remove harmful contaminants like PFAS. 
  • Storage constraints - The average household likely won’t have enough room to store enough rainwater for their needs. 

Rainwater Harvesting FAQ

Is harvested rainwater drinkable?

No, harvested rainwater is not usually drinkable without treatment. However, the quality of harvested rainwater depends on the region and the design of the rainwater harvesting system. In areas with low pollution, rainwater from a well designed harvesting system may be safe to drink. But rainwater in most regions contains contaminants including PFAS, which are associated with health concerns including cancer, immune system problems, and fertility issues.

Is collecting rainwater legal in the USA?

Collecting and using rainwater is legal in the US. However, many states still impose strict rules against harvesting water for drinking due to the likelihood that rainwater contains dangerous contaminants. People who plan to drink their harvested rainwater should install a water treatment system that complies with their state’s policies. 

How does rainwater harvesting save water?

Rainwater harvesting saves water by reducing the amount of water required from a public supplier. Some households are able to rely solely on collected rainwater for all purposes. Rainwater harvesting also reduces the likelihood of flooding by decreasing stormwater flow in the area. 

About the Author

Brian Campbell

Brian Campbell is the founder of WaterFilterGuru.com, where he blogs about all things water quality. His passion for helping people get access to clean, safe water flows through the expert industry coverage he provides. Follow him on twitter @WF_Guru or contact him by email [email protected].

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