• PO Box 25079, Tempe, AZ 85285 USA

How to Harvest and Store Rainwater, Dew, & Frost

A simple 300 gallon water collection system.

Every year, our home collects over 15,000 gallons of rainwater and continually stores over 5,000 gallons of water to grow food. Besides being free, rainwater is also the best water for growing plants. We have even learned the secret to harvest and store dew and frost water, literally water from thin air! Below you will find an instructional video and more detailed info on how we do it.

Instructional Video

Class: How to Harvest and Store Rainwater, Dew, & Frost
Recorded LIVE
When: September 28th, 2013
Who: Dennis McClung
Where: Honeyville Farms in Chandler, AZ
Length: 40 minutes
How to Harvest and Store Rainwater, Dew, & Frost was recorded live in a classroom setting. To be a part of our classes in person, join our meetup group.

Class Handout

[gview file=”https://gardenpool.org/wp-content/uploads/2013/09/Rainwater-Harvesting.pdf”]

How Much Rain Will You Harvest and Store?

The simplest way to harvest massive amounts of water is by using the roof of your home to collect rainwater. Although rainwater from a roof is dirty, it can be used to grow food or purified for potable water use. It is easy to calculate the amount of water your home can collect. You will be surprised to know how much rainwater falls on your home that you can collect, even if you are in a very dry area. Converting your home to collect rainwater is really a simple and inexpensive project that provides a lot of bang for the buck.

It should be noted that you should check with your local government officials to verify that you have the right to collect the rain that falls on your home and if there are any restrictions and guidelines to follow. Residents in Colorado, for example, are not encouraged to collect rainwater, but all new homes in Santa Fe, New Mexico must have rainwater collection systems. Always check with your local officials to avoid problems before you begin planning your project.

We begin the rain collection project by calculating the amount of water your roof will collect during an average year of rainfall by measuring and using some simple math. First, estimate your roof’s length and width. Climbing on a roof is always dangerous and isn’t necessary for this calculation. The easiest way to estimate a roof’s size is by measuring the perimeter of the area that is covered by your roof. Walk around your home and measure the roof’s footprint on the ground. If you have a low pitched roof, the measurements should be pretty accurate. If you don’t have a low pitched roof, add 10%.

My home’s low-pitched roof is about 50 feet long by 60 feet wide, including our carport. Multiply the length times the width to determine the total rooftop surface area. The 50 foot length multiplied by the 60 foot width equals 3,000 square feet. Our family home has roughly 3,000 square feet of surface area to collect rainwater.

Now that we know how much surface area your roof has, we can calculate how many gallons of rain will fall on your roof in an average year. If one square foot of rooftop receives one inch of rainfall, then that equals around .623 gallons. We can multiply the 3,000 square feet of roof we have by .623 to determine that I will collect 1,869 gallons of water per inch of rainwater my home receives!

My city receives less than 8 inches of rain per year. That doesn’t sound like much rain, but if we multiply that times 1,869 gallons of water per inch, we find that my home collects about 15,000 gallons of rainwater per year! Chances are that your area receives much more water than my family’s home in the desert. You will be surprised to learn just how much water falls on your roof.

The Average Annual Rainfall in 10 US Cities

New York, NY       45.73″
Los Angeles, CA     14.78″
Chicago, IL             36.76″
Miami, FL               59.61″
Philadelphia, PA    41.17″
Dallas, TX               35.70″
Washington, D.C.   39.43″
Phoenix, AZ            7.53″
Denver, CO             15.50″
Seattle, WA            38.15″
Inches of Rain per Year  
(Data Source: NOAA)

Install Rain Gutters

The best way to collect the runoff water is to install rain gutters. If your home already has gutters, then that is great as most of the work is already done. Rain gutters are very inexpensive and are really easy to install. Even if your home cannot have rain gutters installed it is still possible to take advantage of rooftop rainfall runoff.

Rain gutter installation is an easy afternoon project with the help of friends and the right tools.

We installed our rain gutters with the help of GP volunteers. We installed the first half of gutters in about two hours thanks to the volunteers. Ask around, you may be surprised that folks you know would want to give you a hand at building a rainwater collection system. There are many folks who would love to get a first-hand experience and to give you a helping hand. It is also a great way to help build community.

When purchasing the materials, avoid galvanized metal gutters as they contain excessive amounts of zinc. It is best to use plastic gutters. Plastic gutters are also cheaper. We found 10 foot sections of rain gutter for about 5 dollars each at our local home improvement store. Our house needed about 10 sections of rain gutters and another 50 dollars in mounting hardware. We installed the gutters so that they sloped about 1 inch per 10 foot section toward our water storage setup. There is not much of a difference between installing rain gutters on your home for conventional reasons versus collecting rainwater. You just want to store the water versus letting it sink in to the ground.

Alternative Roofing

GP volunteers install a new "cool" roof.

You do not have to necessarily replace your roof to collect rainwater, as most roof surfaces are fine, but I had to replace my roofing any way. My home’s shingles were already bad when I purchased the foreclosed home. I decided to use a type of roofing that is easier to use with water collection. I removed the old asphalt shingles and installed a rolled roofing product that is composed of a thick rubberized asphalt base and a reflective aluminum surface. The roofing is great for water collection because it does not have grains of rock and collects much less dust. Do not collect the first batch of rainfall from your new roof to ensure that any aluminum dust has been rinsed from the roofing material. Although aluminum is used in items such as cooking ware, beverage cans, and is even added to salt and flour, you should avoid excessive prolonged ingestion.

No Rain Gutters? No Problem

There may be several instances where you cannot install rain gutters. Certain types of architecture and even HOAs can make it impossible. You can collect runoff rain water and store it in a below-grade storage area by collecting the water on the ground. Take note of where the rain water falls off of your roof and mark it with landscaping markers. Call your utility company to check to see if there are any buried utility lines where the markers are located. Dig a trench that is about 1 foot deep and 1 foot wide. Be sure to slope the trench towards the storage area by around 6 inches per 10 foot span. Use the dirt from the trench to raise the sides about 4 inches above grade. Fill the bottom of the trench with 2 inches of crushed rock and then lay 4” corrugated HDPE drainage pipe, also known as a French drain, so that it slopes in to your below-grade storage area. Make sure the pipe is laid with the holes facing down. Fill the trench with crushed rock to allow for proper drainage to just 1 inch below the surface. Fill the rest of the trench in with the remaining dirt. When it rains, massive amounts of water will flow out of the low end of the drainage pipe. Like the rain gutter method, you now store the water. The water should be stored lower than the low end of the trench so that gravity will fill the below-grade water storage system.

Water Storage Containers

Now that you have enabled your home to collect water, it is time to store the massive amounts that your home will be generating. Collecting large amounts of water is useless unless you have the ability to safely store it for future use. There are several ways to store the water that your home will generate. My home uses several methods to store water. The more places you store water, the less likely you are to accidentally contaminate or lose all of your supply due to leaks.

The quickest and easiest way to store home generated water is to use large containers. You can store as much water as your containers allow and you can even use several containers or add more down the road to increase the overall storage capacity. The most common types of large water containers used for the home are 55 gallon barrels, IBC containers, or even commercial water containers. There are pros and cons to each type of large water storage container. Make sure that the containers are clean and disinfected before using. With all types of large containers, empty and replace with fresh water every couple of years. You also want to make sure that you avoid light and heat while storing water in 55 gallon barrels.

The most common way to store a large amount of water is to use food-safe 55 gallon plastic barrels. Always use food-grade barrels and avoid used barrels that held unknown liquids or chemicals. 55 gallon barrels are great for several reasons. The plastic used in the barrels are the same type of plastic as milk jugs and is safe to use for even potable water storage. They are very durable and can last for many years. They are strong enough, in fact, to hold the 460 lbs of water that it will hold. The tops of the barrels usually have threaded bungs to make accessing the stored water easy. I have a bung wrench and a hand pump specifically designed for 55 gallon barrels. It makes opening and using stored water very easy and secure. One 55 gallon barrel is suitable for a 10’x12′ roof. They will fill quickly.

Another great way to store water is by using intermediate bulk containers, or IBCs. IBC containers are cubic plastic containers that are reinforced with a steel cage and plumbed at the bottom. They are used to ship large volumes of liquids. IBCs vary in volume by holding anywhere between 132 to 792 gallons of water. IBCs can weigh between 200-2,500 lbs when full. Make sure that the location that you decide to keep the full IBCs can hold the immense weight. IBCs can often be stacked and are designed to be palatalized and transported by forklift, but are easy to move and position by hand before filling with water. IBCs do not require a special wrench or pump because they are already plumbed at the bottom with a shut-off valve. Since the shut-off valve is at the bottom, the water flows out with only gravity. Most IBCs are made of white plastic which allows light to enter. Be sure to store in a dark place to prevent algae growth.

There are many great commercial water storage tanks on the market. The amount of water the commercial water tanks range anywhere from 40 to 1,000 gallons or more. I used a tall fiberglass water tank for my rainwater project. I purchased the 300 gallon tank at a local preparedness store for about $350 dollars. I have noticed that most rainwater tanks cost about $1.35 per gallon they hold. If you purchase a 700 gallon tank it will probably cost around $945.

Commercially designed water tanks have many benefits since they are specifically designed for that purpose. Most tanks have well-made plumbing fixtures to easily attach hoses. Water inlets often feature screening to help prevent debris from entering. Some come in many colors or can be painted to match your home. There are also types that can be buried to stay out of sight and maintain a more constant temperature. You will need a pump to access water stored below grade to bring the water to the surface. I prefer the above ground tanks because they easily drain with gravity. If my 6 foot tall water tank is full, then the water exits the water hose with water pressure similar to city water lines. Almost all commercially available water storage tanks do not let light enter so you don’t have to worry about algae growth. Make sure that the lids are kept shut when not in use or screens are installed to prevent mosquitoes from infesting the water.

How to Clean and Disinfect Water Storage Containers

1. If the water storage container is dirty, wash with soap and water and a long-handled scrub brush and rinse well.
2. In a bucket, carefully mix 1.5 cups of bleach and 1 gallon of water. Never add any other ingredients as it may cause unknown reactions.
3. Use a long handle with a scrubber on the end to dip in the bucket and scrub the sides of the water container. Be sure to scrub every inch of the inside of the water container.
4. Dump the bleach mixture and rinse well with fresh water until it no longer smells like chlorine.
5. Allow to air dry before using.

Cisterns and Ponds

Large water storage containers are great, but if you want to store larger amounts of water you will need to store below grade to escape the weight of gravity. There are two main options with subterranean water storage for the home, cisterns and ponds. Both options are capable of storing several thousand gallons of water.

Cisterns are usually used with water wells. Cisterns are large underground storage areas that are usually made of concrete. There is an access hatch on the surface to monitor water quality. Since there is such a large volume of water, contaminates must be kept out. Bacterial contamination is a big concern since the bacteria has a great place to multiply. Cisterns can cost thousands of dollars to have installed, but are a great compliment to any rainwater collection system.

I chose to use a pond to serve as my home’s large volume rainwater reservoir. A pond is much easier and cheaper to install than a cistern. I use my pond to store the excess amounts of rainwater that my home collects and then I use the pond water to supply the Garden Pool. The GP holds about 5,000 gallons of water, but ponds can be made to any size.

A simple way to install a pond is by digging the desired pond size and installing an EDPM pond liner. Be sure that the hole that you dig is free from any protrusions that could puncture the pond liner. If you get a hole, it can be repaired with inexpensive patch kits. If you want a more durable pond, then have a concrete pond installed. If you have an old pool or hot tub that does not leak, then that can be easily converted in to a pond by closing any outlet drains. I have a very large empty pool that would hold over 25,000 gallons of water, but I only use the deep end of the pool to hold 5,000 gallons.

To keep a pond’s water from going bad, it should be have a filtration system. You can filter ponds with mechanical methods such as commercial pond filters, inline UV sterilizers, and chemicals. We opted to use biological filtration methods instead. After our pond was filled, we added fish, pond plants, pond snails, and other elements to create a mini-ecosystem. The fish waste water is purified by the pond plants, aquaponics, and beneficial bacteria.

How to Harvest Dew and Frost

The simple secret to dew and frot water collection.

The secret is out. We harvest dew and frost at the Garden Pool. It is easy to do. Since we are in an arid climate we have to wait for the air temperature to dip low enough to reach the dew point. This happens for us in wintertime, usually in the form of frost. We have a shiny metal sloped-roof that faces east. When the sun melts the frost in the morning, or if enough dew has formed, it travels down the roof in to the rain gutters. That is what you need. It is really that simple.