Rainwater Harvesting 101

Posted by
John Woodard on June 22, 2021
At some point in our lives, we have all tilted our head back towards a stormy sky hoping to catch a falling raindrop in our mouth. But did you know that some people genuinely rely on rainwater as a water source? In arid regions of the world, rainwater is collected to supplement the population’s water needs in a practice known as rainwater harvesting. Although, the practice has gained traction and is now implemented in homes, in agricultural, and in industrial facilities across the world. Below you will learn about rainwater harvesting, how to safely use rainwater, and if a rainwater harvesting system is right for your home.

What is rainwater harvesting?

Rainwater harvesting is the collection and storage of rain for later use for drinking, irrigation, and bathing etc. Rain is collected from the run-off of a structure, such as a roof, and is stored for later use or is redirected underground to replenish groundwater. When rain falls onto a roof, it collects in gutters and downspouts and is channeled into a storage vessel. Rainwater harvesting systems range in complexity from a barrel you may use to water your garden to a large cistern that supplies cooling towers in an industrial facility. Harvested rainwater can even be used as drinking water if treated and filtered properly. There are three basic types of rainwater harvesting systems: rain barrels, dry systems, and wet systems.

Types of rainwater harvesting systems:

Rain barrels

Rain barrels are the most common and economical rainwater harvesting systems. A barrel is placed beneath a downspout and collects rain as it flows from a roof. Most rain barrels hold about 50 gallons of water. If the barrel has a spigot at its base, you can draw water directly from it, attach a hose, or link it to your irrigation system.

Dry systems

Dry rainwater harvesting systems have larger storage volumes than rain barrels, but their premise is the same. A large tank is placed on your property and pipes run from your gutters into the tank, filling it with water every time it rains. They are called dry systems because the pipes dry out between rainfall events and fully empty into the tank thanks to gravity.

Wet systems

Wet rainwater harvesting systems differ from rain barrels and dry systems in that their piping is underground. When it rains, water flows from gutters to underground pipes, and then rises in a vertical pipe into a tank or fills an underground tank. They are called wet systems because the pipes constantly contain water and don’t dry out between rainfall events. Because of stagnant water in the pipes, wet systems are vulnerable to mosquito infestations and anaerobic fermentation. Therefore, it is recommended to screen the pipes and drain them periodically. While wet systems require a little more maintenance than rain barrels and dry systems, they are more aesthetically pleasing since the pipes are underground and the tank can be placed farther from your home.

Do you need a pump for your rainwater harvesting system?

If you would like to use your harvested rainwater inside your home or away from the tank itself, then yes, you need a demand pump for your rainwater harvesting system. A water booster pump is a reliable, flow-based on demand pump that moves water from a storage tank to the intended point of use. A demand pump will pump water out of your rainwater harvesting system and provide the taps inside and outside of your home with pressurized flow. The other option is to simply use gravity to force the water from your tank, but this will limit how you can use your collected rainwater.

Learn More: What is a Demand Pump and How Does It Work? | What is a Water Booster Pump and How Does it Work?

Is rainwater safe to drink?

Rainwater is safe to drink in theory because it is naturally distilled in the atmosphere. However, airborne and surface contaminants can affect the quality of rainwater, so it is not advised to drink it without prior treatment or filtration. As rain falls to the ground, airborne pollutants, such as dust, soot, and atmospheric pollution, contaminate the water. This is especially a concern in urban areas. Also, rainwater absorbs pollutants from roof tops or any surface it encounters before collection. For example, dust, bird poop, bacteria, and pesticides may be on a roof surface and will wash into a storage tank along with the rainwater.

Learn More: What is Distilled Water and Is It Safe to Drink?  | How to Remove Bacteria from Drinking Water

How do you treat rainwater?

You can treat rainwater with a water filtration system or by boiling the water. However, the best water treatment method will depend on which contaminants you would like to remove. It is recommended to test your water regularly, because the composition of your rainwater is subject to change depending on the contaminants present on your rooftop or wherever you choose to collect rainwater. A home water testing kit or a lab water analysis are useful tools to determine what exactly is in your water and to help you choose the best filtration system.

A reverse osmosis system is a comprehensive choice that reduces sediment, volatile organic compounds (VOCs), pesticides and herbicides, and many other dissolved solids. Activated carbon filters also reduce various common chemicals, including gasoline compounds. Ultraviolet purification systems kill waterborne bacteria and viruses. You may even choose to combine a couple different filtration systems to ensure all undesirable contaminants are removed.

While boiling water will kill most parasites, bacteria, and viruses, keep in mind that it will not remove chemicals or heavy metals, and will instead make them more concentrated.

Learn More: What is a Reverse Osmosis System and How Does It Work? | Activated Carbon Filters 101 | What is a UV Water Purifier and How Does It Work?   


How is harvested rainwater used?

Harvested rainwater has both potable and non-potable uses. Potable water is fit for human consumption and can be used to drink, cook, and wash produce with. Non-potable water can be used in any other capacity, such as plumbing, irrigation, and cleaning. Remember that rainwater is only potable if it has been treated and filtered. Below are common uses of harvested rainwater.

    • Drinking and cooking if the water is properly treated and filtered
    • Bathing, laundry, and flushing the toilet
    • Watering the garden
    • Irrigation
    • Filling a swimming pool
    • Washing cars and other equipment
    • Water for livestock and wildlife
    • Industrial uses, such as cooling towers and fire suppression


    Is it legal to collect rainwater?

    It is not always legal to collect rainwater. Many states and municipalities have restrictions on rainwater harvesting systems and the amount of rainwater you may collect. For example, in Colorado each household is only allowed 110 gallons of rain barrel storage. Also, most states prohibit using harvested rainwater for drinking purposes. Rainwater harvesting is not regulated by federal law, so we recommend contacting your local authorities to determine if any restrictions are in place in your area.

    Why is rainwater harvesting restricted?

    Rainwater harvesting is restricted in some areas because harvested rainwater doesn’t go into nearby ponds, lakes, streams, and rivers, which has the potential to disrupt ecosystems. Additionally, rules against drinking harvested rainwater are in place for your safety. Without proper filtration, collected rainwater may contain harmful substances, such as bacteria and pesticides.

    Advantages of rainwater harvesting  

      • Reduces water bills: Relying less on the municipal water supply will reduce your water bill.
      • Sustainability: Using harvested rainwater reduces the amount of a water a municipal supplier must treat and pump to your house, which requires a lot of energy. Treated water can be saved for appropriate uses, such as drinking and cooking, creating a more energy efficient process.
      • Back-up water source in case of emergency: If your normal water source is limited in the event of a drought for example, stored harvested rainwater can provide a back-up water source.
      • Reduces flood risk and soil erosion: Rainwater harvesting lessens stormwater runoff, which reduces flood risk in low-lying areas, soil erosion, and surface water contamination from pesticides and fertilizers that usually enter lakes and streams through runoff.
      • Reduces groundwater demand: As the global population grows, and in turn the demand for drinking water increases, groundwater sources face overuse and depletion. Rainwater harvesting provides an alternative water source and can allow groundwater to replenish.

    Learn More: What is Groundwater Contamination and How Do You Treat It?

    Disadvantages of rainwater harvesting

      • Rainfall is unpredictable: Weather forecasting is not an exact science. Sometimes little or no rainfall can limit the supply of rainwater. It is not recommended to depend on rainwater alone for your water supply.
      • Storage limitations: Once your rain barrel or storage tank is full, it can’t take advantage of future rain events.
      • Regular maintenance required: Rainwater harvesting systems require regular maintenance, because still water is prone to algae growth, lizards, and insects, particularly mosquitoes as they breed in stagnant water. At a minimum, screens and filters need to be cleaned and pipes and storage containers need to be drained periodically.
      • Chemical seepage from roofs: When rainwater is still in the sky, it is clean and naturally distilled, but when it lands on your roof and flows into your rainwater harvesting system, it may absorb contaminants, such as dust, industrial pollutants, pesticides, and bird poop.
      • Potential initial high cost: Depending on the size and complexity, a home rainwater harvesting system will cost between $200 and $5,000. Wet systems with underground piping are the most expensive.


    If you have any further questions about rainwater harvesting or would like to set up your own system, please don’t hesitate to contact us.

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