This article details the components needed to collect rainwater as well as how to calculate the amount of rain you’d be able to collect.
As more of us strive toward a more self-sufficient lifestyle, tried-and-true practices such as food forestry and rainwater harvesting are being re-explored.
But for those less familiar with the rural setting, many of these practices will require a bit of learning.
This article will detail how to collect rainwater for storage and various other uses in a simple, rural home setting.
What is Rainwater Harvesting?
Rainwater harvesting, also known as rainwater catchment or collecting, is the practice of capturing rainfall into an easily accessible storage container that can be used for gardening, washing, cooking, bathing, and even potable purposes.
There are different methods for organizing a rainwater catchment system, but a typical set-up will consist of a large catchment area (typically a rooftop or tarp), a channel for transporting water, and a storage area.
The size of a rainwater harvesting system is largely dependent on the amount of rainfall available in a particular region, the desired amount of water to be collected, and the intended use for the stored water.
This article will explain how to determine the amount of water to collect in the next section.
There are many benefits to collecting rainwater as it provides an additional water source that can be used for numerous purposes. Be sure to read our Introduction to Rainwater Harvesting where we detail the benefits and practical uses for setting up your own catchment system.
How to Collect Rainwater
Rainwater Harvesting System Components
While there are several different ways to set up a rainwater harvesting system, the most basic setup will always have a catchment area, a conveyance, and a place for storage. Some more advanced systems might have a water pump and filtration device for moving large amounts of potable water. We will discuss all of these components in this section.
Roof - The catchment area is the first point of contact for rainwater to be collected into the system. A wide, flat surface that is slightly angled downward works best for collecting the most amount of rain possible. The larger the surface area, the more rainwater will be collected.
In residential setups, due to its large surface area and downslope, the rooftop of a home typically acts as the catchment area. Some harvesting systems have a custom-built catchment area specifically designed to accommodate the amount of rainfall in the region, completely separate from the home.
Tarp - A plastic or vinyl tarp can also be used as a catchment area for rainfall. These are typically laid out on the soil where a collection area has been dug, and a pool of water can be formed as rain falls into it. A conveyance system such as PVC tubing can be used to transport the water from the collection tarp to the storage area.
Because collection tarps are typically used on the ground level, they should generally be placed at an area of higher elevation than the location of the storage tank so as to allow the assistance of gravity for transportation.
As rain falls and collects on the catchment area, a conveyance system is needed to transport it from the catchment area to a collection site. For a rooftop set-up, the most convenient and practical form of conveyance would be the rain gutter which encompasses the roof.
Gutter - Gutters are usually semi-circular or rectangular in shape. They can be made of galvanized steel, aluminum, copper, or PVC. The width of the gutter should coincide with the average amount of rainfall in that particular region, but typically, a wider gutter will allow for quicker, less-obstructed flow. Some gutters have a mesh screen covering the top to prevent leaves and other debris from clogging.
Downspout - The downspout is designed to carry rainwater from the roof to wherever excess water is disposed of, typically a storm drain. In the case of most rainwater harvesting systems, the downspout is what connects the conveyance system to the collection area. As water flows through the gutter, it drops down the downspout and flows into the rain barrel. Downspout height may need to be modified to accommodate the height and size of the rain barrel.
Conduit - Not all rainwater catchment systems are set up with a rain barrel at the end of the downspout. Larger catchment systems might have the collection tank placed several yards away from the catchment area. In this case, a conduit would be needed to transport the rain a much further distance. Conduits are typically made of PVC pipe, which can run along the ground at a downward slope, from the catchment area to the collection tank.
To prevent clogging of debris, usually, by way of twigs and leaves, mesh screens can be placed in areas to prevent this from happening. Lining a mesh screen along the top opening of the gutter will prevent debris from entering the channel. Most rain barrels have a mesh screen at the entrance of the barrel, preventing debris from ever getting into the water supply.
Diverter - While the mesh screens do a good job of preventing debris from entering the rain barrel, it is not uncommon for debris to accumulate and clog up the downspout. A downspout diverter kit is designed to allow debris to continue falling through the downspout and out of the system while water is diverted into the rain barrel.
Be sure to read our article on the benefits of using a downspout diverter, the different types available, and where to buy one.
The collection area is where all the water is gathered, stored, and accessed for later use. The most common and safest type of collection unit are food-grade, polyethylene plastic barrels specifically designed for rainwater collection. Plastic is the most practical material for rainwater collection for its durability,
Rain barrels come in various shapes and sizes, ranging from 35-gallon rain barrels for small homes to 1000+ gallon water tanks for small communities.
We've written an article that features reviews of the best types of rain barrels available as well as how to select the right one for your system.
Water pumps provide additional pressure for many water applications, and therefore, broaden the means in which the water supply may be used. In a rainwater harvesting system, the right water pump can allow for a significant increase in flow rate which may help for gardening, washing, and even indoor purposes such as bathing and cooking.
Water pumps range widely in size and power; thus, selecting the correct pump for your application is critical to ensuring a properly functioning system. Above-ground jet pumps work by suctioning water from the tank through a hose, while submersible pumps create pressure by being submerged in the water tank, pushing water outwards.
The pump should be installed in close proximity to the storage tank. Whether it be a submersible or jet pump for outdoor or indoor use, the pump will create pressure so that the water supply can be used for a variety of other purposes.
Be sure to read our article on rain barrel pumps to learn more about how to choose the best fit.
It can be noted that most rainwater harvesting applications are set up for outdoor use, namely for irrigation, gardening, and outdoor washing. But with the right setup, an indoor application can be set up for cooking, bathing, washing, and even drinking. For these purposes, a proper post-filtration system is necessary to remove potentially harmful contaminants.
Filtration systems vary greatly. Sediment filtration systems will remove particles of debris, making the water suitable for bathing and cleaning, while UV filters will remove harmful bacteria, making it safe for consumption. The type of filtration system needed will depend greatly on the household’s needs.
Be sure to read our article on rainwater filtration systems.
How Much Rainwater do I Need to Collect?
Catchment Size and Rainfall
There are two main factors to consider when determining the volume of water you’d be able to collect with your rainwater harvesting system. That is, the size of the catchment system in square feet and the average amount of rainfall in inches for that particular region.
For residential rainwater harvesting systems, the rooftop of the home is the most effective and practical means for catching rainfall. Its large, angled surface area allows for easy contact and transportation of rainwater. The larger the roof, the more rainfall will be harvested.
As a general rule of thumb, the following equation can be applied to determine, roughly, the amount of water that can be gathered according to roof size: 1" of rain x 1 sq. foot = 0.623 gallons. That is, every inch of rain multiplied by 1 square foot of catchment area will equate to about 0.6 gallons of stored water.
Innovative Water Solutions has a simple calculator to determine the amount of rain that can be collected depending on roof size and average annual rainfall. Find the calculator here: https://www.watercache.com/resources/rainwater-collection-calculator/
U.S. climate data has additional info in determining average annual rainfall in each region: https://www.usclimatedata.com/
The size of the collection tank should reflect the amount of water intended to be used from it. Estimates vary greatly, but according to the USGS, the average person in the U.S. uses about 80-100 gallons of water per day, 30 percent of which is outdoor use.
Assuming that the majority of water usage for a particular household will come from either the city water supply or a well, one can still gather a rough estimate of the amount needed from rainwater storage based on its intended usage. Most rainwater systems are intended for outdoor use, such as gardening and washing. This need, compared to the amount of rainfall that can actually be collected, brings us closer to determining the appropriate rain barrel size.
It is best practice to select a rain barrel size that is large enough to store the right amount of water for its intended use but not too large that it allows unused water to sit for an extended amount of time. Untreated, stagnant water may lead to pests and contamination and will require further treatment.
Let's create a scenario as an example: 15 inches of rain over the course of the year on a 1,000-square-foot roof in Southern California would yield 9,345 gallons of rainwater.
Since it certainly doesn't rain year-round, a conservative estimate would be to divide up the annual collection over the course of a rainy season, say four months. This brings the potential amount of collection to about 2,336 gallons each month for four months.
While it's tempting to decide to purchase a 2,000-gallon tank to maximize storage potential, factoring in the amount of usage for the water supply may bring the tank size down significantly.
A small family estimates that they will use about 2,000 gallons of water per month for gardening, washing their cars, and other outdoor uses. The 2,000-gallon need, divided by 30 days, averages out to about 66 gallons of water per day. For this particular scenario, a rain barrel between 50 to 100 gallons will be quite large enough.
There certainly are a myriad of other factors involved in determining the exact size of rain barrel needed. A popular strategy is to start with a smaller rain barrel that has an overflow valve. If additional storage space is needed, more rain barrels may be linked together via the overflow valves. This eliminates the error of overestimating the need and purchasing too large of a container.
Major Considerations for Collecting Rainwater
Despite some common misconceptions circulating online, there currently aren’t any laws that explicitly prohibit rainwater harvesting in any of the 50 states. Some states certainly have some restrictions in terms of quantity and purpose of usage, but if all statutes are adhered to, anyone can harvest rainwater in their state of residence. Be sure to check your state legislation before setting up a rainwater harvesting system to make sure all regulations are met.
We’ve written a detailed article that lists rainwater harvesting laws for each state in the US, along with links to their respective government websites. We update it regularly, so be sure to check it out here.
Location and Set Up
Catchment - Whether the designated catchment area is on the roof of a home or a tarp on the ground floor, the catchment area should always be elevated higher than the storage area. Gravity will allow rainwater to flow to the designated storage area when it is placed at a lower elevation.
Rooftops, by default, will already be higher than the storage area at ground level, thus, gravity will already work in your favor. In the case of a tarp, select an elevated level of ground to place it on, preferably at the top of a hill.
Rain Barrels - For rain barrels without a pump, the water pressure coming from the spigot will be much greater when slightly elevated above the ground. Place the rain barrel on cinderblocks or bricks to allow gravity to aid the force of water as it comes out of the spigot and through the attachment hose.
The end of the downspout should lead directly into the top of the rain barrel. Find a level, secure location underneath the downspout for where the rain barrel can reside.
In the event that the rain barrel cannot be placed near or underneath the downspout, perhaps due to the structure of the home or the size of the rain barrel, additional gutter attachments may be needed to extend the downspout toward the opening of the rain barrel.
While one may be tempted to collect as much water as possible to store for future usage, it is best practice to use just enough for frequent usage. Having large amounts of stagnant water sitting for long periods of time can collect debris, grow algae, and attract mosquitos.
But even with an adequate-sized barrel, routine maintenance, and cleaning should always be applied. Clear the mesh screen frequently for leaves and other debris that may gather, and be sure to check the downspout for any blockage too.
In regions with very cold winters, be sure to drain the barrel of all water to avoid freezing. This would also be a good time to do a yearly cleaning of the inside of the barrel. Take a hose and rinse out the inside of the barrel, and clean all the connection ports.
During the summer months, mosquito repellant drops can be applied to prevent the growth of larvae in the barrel.
Rainwater collection is a very easy, practical, and cost-effective method of storing additional water reserves for a variety of uses. A typical rainwater harvesting system will consist of a catchment area, conveyance, and storage area. Additional features such as a pump and filtration may also be installed. Finally, be sure to calculate how much water you'd be able to collect to determine the size of the rain barrel you'd need.
Thank you for taking the time to read our article on how to collect rainwater. We'd love to hear your feedback in the comments section below.
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