A comprehensive guide

What is rainwater harvesting?

Rainwater harvesting is the collection and storage of rain, captured for usage later from a variety of surfaces including roofs, catchments, streams, and air.

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Whether you’re interested in being more environmentally responsible, going off-grid, or reducing your water bill, rainwater harvesting is an excellent home improvement project to undertake. With a little knowledge and some easily accessible equipment from your hardware store, you can build a complete rainwater harvesting system to help you store hundreds of gallons of water.

While it’s simple to get started, more complex systems are entirely possible and the potential impact it can have on your life and your wallet is hard to ignore. You could go so far as to replace your municipal water supply entirely with rainwater (though you would want to filter it first if you plan on using your collected water for drinking).

31,620 gallons gallons the average house can collect every year

Don’t be intimidated by how complex it can be though, this ancient practice began with literal holes in the dirt. It can be as simple as a barrel at the end of a downspout.

Whatever your goals are, this comprehensive guide to rainwater harvesting is a great place to start to understand where to begin and the things you’ll need to know throughout the process of setting up your own system.

How Much Water Can You Collect?

I’m sure your interest was piqued when I said that you could potentially use harvested rainwater as your primary source of water supply and it’s true! It does depend on how much rainwater you can collect though and that depends on a whole host of factors that ultimately come down to two questions:

  1. What surface are you using to collect rainwater?
  2. How much rain falls where you live?

These numbers will vary per person and the answer to how much water you can collect will be different for each person. Still, based on the average rain fall in the US, and the average roof size in square feet (the most common catchment area), you can collect around 31,620 gallons a year. The average US household of four uses 300 gallons a day, or 109,500 gallons a year. 

This number is just how much rainwater you can collect from your roof though. Even though it’s the most common, and the easiest, there are other ways that you can collect rainwater. If you need to, you can find other ways to augment this amount to collect even more.

If you want to figure out how much rainwater YOU can collect from your roof, check out our rainwater harvesting calculator that will help you find the numbers you need to know what you can expect.

Rainwater Harvesting vs. Grey Water Recycling

If you’ve heard of rainwater harvesting (and by this point, I hope you have) it’s likely you’ve heard of grey water recycling too. Both are excellent ways to help reduce your dependency on municipal water but are very different things. 

A grey water recycling system collects relatively clean water that you’ve already used and treats it for reuse within the home. Some common sources of greywater include baths, showers, sinks, washing machines, and kitchen appliances. Of course this water needs to be treated in order to be reused, it’s still relatively clean and can help reduce your dependence on water. Still, it’s relatively easy to collect as the sources are concentrated

Rainwater is actually clean as it falls (it’s even drinkable) and won’t need to be treated, but you’ll need a catchment area in order to collect it. Rain falls over a wide area so if you want to collect it, you’re going to need to cover a lot of surface area. For those who already have roofs, this is relatively simple making rainwater harvesting very attractive.

Is it legal to harvest water?

Collecting rainwater couldn’t possibly be illegal could it?

It turns out that, in more than a dozen states, it can be illegal to varying degrees. The main argument against harvesting rainwater is by collecting rainwater, you are denying someone further downstream the rights to that water. In Colorado, in particular, a 120-year-old law implies exactly that, making it illegal to collect rainwater there. And water rights are a serious topic, especially when you start to consider its impact on agriculture or the pending shortage of freshwater.

Before you setup a water harvesting system, be sure that you are aware of any laws or restrictions that may impact what water you can collect, or whether you can at all!

Benefits of rainwater collection

There are a myriad number of ways that collecting rainwater is beneficial, some of which are obvious and others less so. The most clear reason though, is to help address and prepare for the pending freshwater crisis. With over 2 billion people around the world experiencing water scarcity for at least 4-6 months of the year, we all need to contribute to the solution while also making sure we have water for ourselves. Still, here are the 5 main benefits of collecting rainwater

  1. Conserve water
  2. Reduce demand on groundwater
  3. Recharge groundwater
  4. Reduce your water bill
  5. It’s better for plants (if you garden)

These are really only the 5 main reasons but there are plenty others, depending on how you plan on using rainwater or where you live. The US is already starting to see water shortages so even if you live in the US, you may already be feeling the effects of water scarcity. If you’re still not convinced, you can read about these benefits in more depth here.

Uses for Rainwater

The potential uses for rainwater are limitless. Anywhere you would typically use water, you can use rainwater. Still, depending on your needs, some uses are going to require more complex systems than others.

For example, if you plan to use what you’ve collected in your kitchen faucet, you will need to improve the water quality so that it is drinkable (also referred to as potable water). Additionally, you’ll have to perform regular maintenance on whatever contraption you’ve setup to store rainwater so that algae doesn’t bloom, bacteria doesn’t flourish, or mosquitos don’t lay eggs in your storage container or barrel.

Some of the most common uses for rainwater include watering lawns or gardens, setting up irrigation systems, providing for outdoor water features, flushing toilets, and washing vehicles to name only a few. Be sure to consider how clean your water needs to be before using it though. For example, you won’t need expensive filters to use water in your garden or wash your car.