In this Rain Tanks Series: Rainwater Harvesting 101, we will look at an introductory overview of the rainwater harvesting practice, definition of terms, regularly used equipment, and will consider the difference between active and passive systems. To define rainwater harvesting: rainwater harvesting is the practice of capturing rainfall and using it as an alternative water source to supply water for water-requiring activities around or inside a property.
Harvesting rainwater is either active or passive in practice and can also be known as rainwater catchment, rain harvesting, rainwater collection, abbreviated RWH, and setups are known as rainwater harvesting systems, which can be abbreviated RHS for short.
Active vs Passive Rainwater Harvesting
Active rainwater harvesting is the practice of directing the rain from the surface it lands on and into a container for storage where the water can be used when needed.
Passive rainwater harvesting is practiced without a storage container and is done when rainfall is channeled from a surface directly to a point of use, such as a pond, rain garden, landscaping, berms or low spots on a property.
Between active and passive, active rainwater harvesting is more common and the method most rainwater harvesters choose to practice.
What is Needed to Harvest Rainwater
To be a successful rainwater harvester, you will need, (at least), a catchment area, a conveyance system, and a collection container. These are known as the 3 C’s of Rainwater Harvesting: catchment, conveyance, and collection. Other rainwater accessories and equipment may be recommended or needed depending on how clean, efficient, and overall effective the RWH system is wanted.
In rainwater harvesting, the term Catchment Area refers to the surface that the rain falls on and is used to collect rainwater from. A catchment area can be any surface that allows rainwater to easily flow over it without being absorbed and from where the rain can be directed to the point of collection or use.
Catchment areas are most often the roof of a building, and most commonly the roof of a home or business. The roofs of sheds, pavilions, garages, warehouses, equipment yards, barns, greenhouses, and livestock houses are other common rainwater harvesting catchment areas. Non-roof type catchment area examples include pavement such as parking lots, streets and roadways, tarps, rocky surfaces and outcrops.
The best catchment area for rainwater harvesting is any impervious surface that rain will not soak into and is made from materials that will not contribute debris, leach any chemicals, will resist growth of moss or mold, can be cleaned, and easily washes away any foreign debris that has accumulated on the catchment surface. Seam metal roofing made from finished steel is the top recommended material and choice for a rainwater catchment area. The second-best choice are slate tiles, followed by composition shingles, EPDM coated roofs, and lastly asphalt shingles.
In rainwater harvesting, the term Conveyance System refers to any object or series of objects that can be used to channel rainwater as it flows from the catchment area to the collection container or containers. A conveyance system should be able to successfully contain, control, and direct rainwater. Conveyance systems are most often gutters, downspouts, and plumbing such as PVC pipe.
Gutters and downspouts are a common choice as they are typically already installed on buildings to direct rainfall away from the structure’s foundation. Gutters and downspouts can be easily modified for use in a RWH system and customized with rain harvesting accessories. Vinyl and galvanized steel are the preferred guttering material types.
Plumbing such as PVC pipe is most often used to replace downspouts or used to extend the reach of the conveyance system. Plumbing is used when the rain collection container cannot be placed directly next to a building, when multiple downspouts are to be connected, to connect multiple tanks together, and to connect the RWH system to additional equipment or fixtures for use.
When shopping for PVC pipe, it is recommended to use ANSI/NSF 61 and/or ANSI/NSF 14 certified PVC pipe to ensure the plumbing is approved for potable water and will not impact the quality of your rainwater harvest. This recommendation stands even if the rainwater is not intended for potable applications.
Pre-Tank Filtration refers to rainwater harvesting accessories that are installed in the system before the collection container and are used to improve the cleanliness of the rain by removing debris and some contaminants. Examples of pre-tank filtration include downspout screens, first flush diverters, and tank screens. Pre-tank filtration is used to provide cleaner, higher quality rainwater as it is being collected and to reduce the overall amount of system maintenance required.
A downspout screen, also known as a leaf eater or rain head, is one of the more commonly used pre-tank filtration accessories. They are built with an open top, fine mesh screen, and bottom port connector designed to screen out and remove unwanted debris while allowing rainwater to flow through. Downspout screens can only be used to remove large debris such as sticks, leaves, other plant matter, animals and insects.
Downspout screens are often used as they are easy to install, simple in design, and effective. They are made for placement within the downspout of the RWH conveyance system.
A first flush diverter is also a common rainwater harvesting accessory added on to improve the quality of collected water. The first flush diverter is also known as a roof washer as it is used to collect and flush away some of the first rainwater during a rain event that washes debris from the roof and is therefore often the dirtiest and most contaminated. This accessory can be used to remove materials that a downspout screen cannot remove such as sediment, animal droppings, pollen, any potential chemicals or other finely sized materials.
A first flush cannot be used exclusively to completely remove and prevent some dissolved contaminants from reaching the rain container for drinking quality water.
A tank screen is a fine mesh basket filter made to fit in the manway opening on bulk volume rainwater tanks and catch debris immediately before it reaches the container. A tank screen comes standard with many polyethylene rain tanks when purchased and is effective in removing large debris and anything that another pre-tank filtration accessory may have missed.
When all three pre-tank filtration accessories are used together in a rainwater harvesting system, the chances for debris, unwanted materials, insects or animals reaching your collection container becomes much more unlikely.
The Collection Container is the most important part of an active rainwater harvesting system – without it, every gallon of rainfall will go to the soil rather than be captured for use. Rainwater collection containers include rain barrels, polyethylene rain tanks, underground poly cisterns, galvanized steel rain tanks, stainless steel rain tanks, and IBC totes. All of these container types are commonly used in the practice of rainwater harvesting.
Rain harvesters will choose one container type over another based on the total water volume they need, what the rainwater will be used for, available property space, and budget limitations.
Rain Collection Container Types
- A rain barrel is smaller in size and volume capacity, often ranging up to 100 gallons. Rain barrels are ideal for small volume needs, outdoor uses, properties with limited space, and those looking to harvest rainwater on a low budget.
- A polyethylene rain tank has a wide range of sizes and storage volume, often ranging from 100 gallons up to 10,000 gallons. Polyethylene rainwater collection tanks are ideal for long term reliability, are lightweight, low in cost compared to metal, and are suitable for all rainwater harvesting applications.
- An underground poly cistern has a rainwater storage range up to 20,000 gallons and is ideal for long term use, properties with limited aboveground space, and when the benefits of underground installation are desired such as protection from freezing temperatures and algae growth.
- A galvanized steel rainwater tank is often the choice for storing very large volumes of rainwater in a tank capable of lasting for decades. Having a volume range up to 100,000 gallons, or more, galvanized steel rain tanks provide one of the largest storage volumes available, but also have a higher purchase price and most often require professional installation.
- Stainless steel rain tanks are made from high quality metal and can last a lifetime, but due to the material are often a more expensive option and one with a lower total available volume range.
- An IBC tote is a shipping, storage, and application container popularly repurposed and used by DIYers for rainwater harvesting or other alternative projects. The polyethylene caged IBC tote with 275 gallons or 330 gallons capacity are the common choice for RWH systems. An IBC is popular as they provide a large volume with a lower cost, are lightweight, easy to modify, and can be purchased secondhand or as a rebottled IBC tote for less.
Additional Points on Collection Containers
In rainwater harvesting, a collection container can be any watertight vessel made of any material to any shape and volume size. It is simply important to ensure the container’s material, shape and volume match the needs of the use and layout of the property.
The material the rain container is made from should be safe to store rainwater long term, should not leach chemicals into the rainwater, should not break down, rust, leak, or rupture. The most common materials used for rainwater collection containers are polyethylene plastic and metal. Earthen materials such as concrete are also sometimes used.
The collection container should also be kept closed, vented, and include fine mesh screens at every opening to prevent access by animals and insects such as mosquitoes. Preventing mosquitoes from breeding in your rain tank is an important and responsible measure for all rainwater harvesters and is even required by local regulations in some areas of the United States.
Most bulk volume rainwater collection containers commercially available for sale are designed and made from materials that cover these points to ensure the container is safe, reliable, and approved for rainwater harvesting. Current polyethylene plastic rainwater containers are made using U.S. FDA approved materials and are NSF/ANSI 61 certified for potable water applications.
RWH Collection Container Improvement Accessories
RWH Collection Container Improvement Accessories are tank add-ons made to improve storage effectiveness, water quality and reduce maintenance. Examples include the solar shield, tank screen cover, and water level gauge.
The solar shield is a dual-function accessory designed to inhibit the amount of sunlight that reaches the stored rainwater through an open manway and also acts as a calming device and water brake to slow the inlet of rainwater as it flows into the tank. A solar shield will help to prevent algae growth and the resuspension of sediments.
The tank screen cover is exactly as it sounds: a cover for the rain tank screen. A tank screen cover is a lid that fits over a tank screen filter to completely block out sunlight while still allowing rainwater inflow through plumbing port holes built into the cover. Limiting sunlight is an important step in reducing algae in a water tank.
A rainwater tank gauge is used to allow an owner to easily see and monitor the current water volume in their collection container without having to open and look inside the tank. Common rainwater tank gauges are mechanical, non-electrical volume gauges that use a float and/or weight balance system that changes the reading on the tank gauge as water levels in the tank change.
A Water Pump is a specialized piece of equipment, often electric powered, that is used in RWH to increase the speed and force strength of rainwater as it is being drawn from the collection container. Speed refers to how fast the water moves through a pipe or hose and is listed on water pump products as flow rate in gallons per minute (GPM). Force strength refers to how much output power the water will have and is listed on water pumps as pressure in pounds per square inch (PSI). A water pump can have a high flow rate with a low pressure output, and vice versa.
Water pumps are made in a variety of designs and capabilities and are an optional part for many personal rainwater harvesting systems but are required in many specific applications. A water pump is used in rainwater harvesting to increase the rate water is withdrawn for filling activities, to increase water pressure so equipment can be used with the RWH system, or both. To use rainwater with a higher pressure sprinkler, spray irrigation system, spray nozzle, or with post-tank filtration and treatment equipment, a water pump will be necessary.
Also, if rainwater is to be used indoors, a water pump is needed to provide enough water flow and pressure to taps and appliances for them to properly work.
Post-Tank Filtration refers to rainwater filtration, purification, and/or treatment equipment that is positioned after the collection container in the RWH system and before the point of use. Similar to a water pump, post-tank filtration may not be necessary depending on the use and is only needed for specific rainwater applications.
Examples of post-tank filtration include sediment filters, carbon filters, multi-stage cartridge filters, ultraviolet (UV) light water treatment systems, chemical dosing systems, ozone generators, and direct chemical-water treatment.
Post-tank filtration options will require the addition of a water pump in all instances for proper equipment operation except for chemical dosing systems, ozone generators, and direct chemical-water treatment with chlorine (bleach / sodium hypochlorite).
To achieve potable (drinkable) rainwater from harvesting, the recommendation is to use an ANSI/NSF 53 certified multi-stage cartridge filtration unit with sediment and carbon filter rated down to a 5-micron pore size and an ANSI/NSF 55 certified Class A ultraviolet (UV) light treatment system. For more info on making rainwater safe to drink, see our blog post here.
Takeaway | Rainwater Harvesting 101
It is our hope this guide to Rainwater Harvesting 101 has helped you with an overview of the rainwater harvesting practice, provide definitions and examples of the common components required to successfully harvest rainwater, and has helped in whatever step or stage you are at in planning, preparing or implementing your own rainwater harvesting setup. We have a wide selection of rain harvesting accessories and rainwater collection tanks available for implementing a full-scale, effective and efficient rainwater harvesting system. If you require any assistance in selecting the equipment you need, reach out to our product experts who will be glad to help.