Rainwater Harvesting Guide for Beginners

Robin Greenfield getting water from a tank with a bucket, outside his tiny house.
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This is a rainwater harvesting guide designed to answer basic questions and break down the barriers that many people experience with rainwater harvesting. Rainwater harvesting is easy, simple and free. Unfortunately there are a lot of misperceptions out there that have resulted in people thinking that rainwater harvesting is complex or illegal. A five minute investment of time on this page will clear up these misperceptions and can get you harvesting rainwater today!

Let me start off with settling one of the most common misunderstandings of rainwater harvesting in the United States. “Rainwater harvesting is illegal.” This is false. True, a tiny percentage of municipalities have regulations or laws against harvesting rainwater. There have been some viral stories about the absurdities of these laws, and unfortunately some have spread misinformation that has resulted in people thinking that laws against harvesting rainwater are widespread. They are not. They are the exception. Never assume rainwater harvesting is illegal.

In fact, I have had countless people tell me that rainwater harvesting is illegal in San Diego, California where I lived for five years. Not only is it not illegal. It is encouraged by the city government and they actually provide financial assistance to help more people harvest rainwater.

Another common false belief is that rainwater harvesting is not possible in climates that receive minimal rain, such as the desert, Southern California or Mediterranean climates. In fact, these are some of the best places to harvest rainwater. Every climate is an appropriate climate for harvesting rainwater. To give you an example:

Southern California gets about 10 inches (25 centimeters) of rain per year. A desert is classified as receiving less than 10 inches per year.

The average size house in the United States is about 2,000 square feet. The roof square footage of the average size house is about 1,700 square feet. In this region the average household could harvest over 10,000 gallons (40,000 liters) of water per year. That is a very meaningful and substantial amount of water! Here is an online calculator. When I lived in a tiny house in San Diego, my sole source for water at home was rainwater and it was during the mega-drought. Here is a video that shares my rainwater harvesting and living situation there.

The formula is very simple: roof area (ft2) x precipitation amount (inches) X 0.623 = amount collected (gallons)

If you insert yearly rainfall into this formula you get the amount of rain that you could generally expect to be able to harvest in a year. Of course you don’t need to pay any attention to this formula in order to successfully harvest rainwater

Many, believe that rainwater harvesting is complicated or expensive. This is false. Anything can be made complicated or expensive, but rainwater harvesting is not inherently complicated or expensive. The simplest form of rainwater harvesting is to place any container underneath the drip line of a roof without a gutter for the water to collect. The water that drips off the roof will simply collect into the container, such as five-gallon buckets, clean garbage cans, plastic totes, etc. For those that have gutters on their homes, it is as simple as directing the downspout into containers.
The containers I recommend the most are 55-gallon drums and 275-gallon IBC totes. Both of these can be seen in my Orlando, Florida tiny house tour: 55 gallon drums setup – 275 gallon tote setup. 55 gallon drums can be purchased for about $15-$25 on craigslist and 275-gallon totes are generally around $100 but I have seen them for closer to $50 when purchased in larger quantities (these prices could fluctuate). I purchase food-grade drums and totes that were used to deliver foods, organic shampoos and other non-toxic products. The 275-gallon totes have spigots on them that work perfectly for filling up five-gallon buckets. Adapters can be connected to the spigot to connect a hose as well.
You can purchase rainwater totes that are marketed as totes but they are generally much more expensive than repurposing. There are also tanks that can store thousands of gallons that can be a good investment for the right situation. 5,000 gallon storage tanks are commonplace in many regions of the world.
Some worry about mosquitos breeding in rainwater tanks and see this as a reason not to do it. This is a simple solution, keep the rain containers sealed off from mosquitos. Most tanks have just a small opening on the top and screen can be put over this opening to prevent any mosquitos from laying eggs in the water. However, it is not actually an issue for mosquitos to lay eggs in the water. The issue is if the eggs hatch and the larvae go through the entire process to become adult mosquitos. This takes a minimum of seven days but as much as a few weeks, all depending on water temperatures. (Warmer temperatures have shorter life-cycles than colder temperature water.) What this means is that if you harvest rainwater in buckets with no screen over the top, you simply have to make sure to use the water and empty the container fully within one to two weeks, so the larvae can’t turn into adults. The mosquito larvae die once they are poured onto the soil as they are an aquatic larvae. They then fertilize the soil and plants in a garden. By following this no mosquitos will be bred whatsoever.
Some worry about algae growing in the tanks. Algae poses no problem if you are using the water for your garden. The algae will simply fertilize the garden. Even for showering or watering dishes the algae isn’t a problem. The simple solution to prevent algae growing in tanks that have longterm storage is to seal them from light. Without light algae won’t grow.
Rainwater can be drank directly from the sky. The issue is what bacteria, algae or contaminants might be in the container that the water is stored in. I love drinking rainwater and I purify mine through a Berkey filter.
In this video I demonstrate and explain using the Berkey Filter with rainwater. Of course, rainwater harvesting for the garden is an easier first step than harvesting it for drinking water.

The amount of rainwater you are able to harvest depends on your storage capacity. So, I mentioned that an average sized household in the desert can harvest over 10,000 gallons of water per year. But most people would not have storage to harvest it all. You don’t need 10,000 gallons of storage to harvest 10,000 gallons of water. Timed correctly, 1,000 gallons of storage filled 10 times could capture all 10,000 gallons of rainwater that falls on a roof. That would take four 275-gallon totes or twenty 55-gallon totes. But even just one 275-gallon tote could harvest over 3,000 gallons in a year. Pumps can be hooked up to distribute the water.

Passive rainwater harvesting makes it much easier to store thousands of gallons. This could be via digging a pond on site. Or it could be directing water from the rooftop directly to the garden or landscape. The soil can be a passive water storage and done correctly can be held for months and create resilience against droughts.

Raising your containers utilizes gravity to create water pressure. The higher the tank, the more water pressure is created. A hose can be connected to the raised containers to easily water a garden. With 275-gallon totes I raise them up two cinderblocks high so that I can put a five-gallon bucket under the valve for easy filling. Drip irrigation can be connected to totes, but it is more challenging. Large, passive irrigation systems can be created with large storage.

In summary, any amount of rainwater harvesting is a meaningful amount to harvest. You can start small and harvest more each year and at the same time increase your garden size. Some of you may decide to become water independent by maximizing your rainwater harvesting while some of you may decide to get a single 55-gallon tote or stick some buckets under your roof drip line. Rainwater harvesting is simple, safe, easy, affordable, legal and a human right. Don’t forget it! Share this message with others!


My guide on how to use water wisely


Blue Barrel Systems “your one-stop shop for do-it-yourself (DIY) rainwater harvesting”

Take a look at the systems I used on a typical suburban home in Florida:

Take a tour of my Florida tiny house during 2018-2019 where I lived primarily on rainwater.

Harvesting rainwater with a 275-gallon tote. Filling up a five-gallon bucket to water the garden with:

Watering the garden with rainwater using a five-gallon bucket:

A basic outdoor shower I created using a 275-gallon tote:

An outdoor kitchen I created using a 55-gallon drum to supply rainwater for my sink:

Drinking purified rainwater from a Berkey filter in my outdoor kitchen:

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