The basic concept of rainwater harvesting has been employed throughout human history: to capture and manipulate atmospheric moisture in the form of local precipitation. The design and technology of rainwater systems, however, have increased over time in their ability to provide sufficient volumes of water and the reliable purity of that water for modern uses.
At its simplest, the practice of rainwater harvesting (often abbreviated RWH) is the capture and storage of regular rainfall so it can be used for a desired application. At its fullest, approaches in modern rainwater harvesting engage the use of multiple system components to effectively collect, decontaminate, store and deliver water clean enough for its intended uses including freshwater for drinking and other potable applications.
The complete range of individual components needed can vary based on the specifics of the RWH system and its location. Successful RWH systems will include a rain tank, additional components, equipment and various rain harvesting accessories that define the difference between a sub-par rainwater harvesting system and one that gives you water good enough for potable uses.
Individual Components of Successful Rainwater Harvesting Systems
In this Rain Tanks Series post, we will review nine (9) distinct parts and components that are necessary for or contribute to a successful rainwater harvesting system. We will explore each part individually from the initial point of rain contact up to the desired end use of the captured rainwater.
Catchment Area
The catchment area is the first point of interaction between the sought-after rainwater and the entire RWH system. Catchment areas are used to convert what would otherwise be simple rainfall into a harvested resource and serve as the dedicated location for catching and diverting the incoming rainfall.
Catchment areas are often the roofs of homes or businesses, but they can be any structure and can be any size, shape, angle and/or material. Other common rain catchment areas include sheds, barns, livestock houses, warehouses, as well as specially built structures and rain funnels. The specific characteristics of a catchment area can affect the resulting water volume and its quality.
- Larger catchments allow for more water collection, and the opposite is also true.
- Shape is not a factor as long as flowing rainfall is delivered to a channeling system.
- Exceedingly steep roofs can cause water loss due to potential runoff from increased water velocity.
- The material the catchment is made from is important to the resulting quality of the water.
- Asphalt shingle and earthen roofs can contribute elements or break-off particles that may need to be filtered out.
- Wooden roofs hold greater potential for microbial growth, algae, and mold that can be carried into a RWH storage tank.
- Metal roofs and polymer-coated roofs are best for RWH systems as these materials are the most hygienic and resistant to the chemical effects of rainwater.
To know how to approximate total rainwater volume capture based on catchment area, see our Rain Tanks Series post How Much Rainwater Can I Collect with Rainwater Harvesting.
Rainwater Channeling and Gutter System
After the catchment area, rainfall must somehow be successfully directed to a point of storage or use rather than to the ground where it will be absorbed or evaporate. A rainwater channeling system at the low points of a catchment area can accomplish this, where roof gutters and pipes are commonly chosen and used to channel water for many RWH systems.
Similar to catchment areas, gutters can be made from various materials. They can range from wood to metal to synthetic materials. Metal and synthetic materials such as vinyl and plastic have the greatest preference for rainwater harvesting scenarios.
The best RHW gutters will include screen covers that limit or restrict organic matter from making it any further downstream. The key to successful water channeling systems is to gently slope the gutters toward the tank collection point and ensure all water runs together for any needed pre-storage filtering or flushing.
Rain Heads
If gutter screens are not used in a rainwater harvesting setup, accessories known as rain heads become an important component in total system cleanliness and maintenance. Rain heads, also known as leaf eaters, are made to install in gutter downspouts and function as inline filtration units. They provide an open section in the rainwater channeling system for rainfall to pass over a fine mesh screen.
The rain head filtration screen effectively captures organic matter before it can flow downstream into the tank. Leaves, sticks, parts of animals and the like are all caught by the rain head and remain on the screen to allow manual removal or get flushed off by moving rainwater.
Without a rain head, this collection of material debris in the rainwater could otherwise cause a problem. It could end up in the rain tank, clog plumbing or accessories, or remain within system wet points and contribute to microorganism growth as it decays over time. When there are no other pre-tank screens, many consider rain heads to be an integral part of simplifying the work and maintenance of rainwater harvesting.
First Flush Diverter
Similar to rain heads, first flush diverters can be an important component of a clean and healthy rainwater harvesting system. A first flush diverter by definition will take the initial influx of water up to a specified volume or time lapse and discard it as waste. This RWH accessory can be a specially designed product, an outlet valve capable of being opened and closed as required, or any other improvised method.
The purpose of the first flush accessory is to keep the first volume of rainfall from reaching the storage tank as it flows through and cleans the system. This is an important step whenever seeking to harvest clean rainwater because the first rainfall that flows over the catchment area often contains the most materials capable of affecting collected rainwater quality. Example materials often flushed by the diverter include animal excrement, dead animal and plant matter, any associated microorganisms, bacteria, as well as dissolved elements and sediments.
Additionally, the first interval of rainfall effectively scrubs the atmosphere of any suspended pollutants from industrial processes, commercial activities and combustion exhaust. Potentially contaminating particles, molecules, and/or gasses can get dissolved and carried down in the first rain that falls on a harvesting system. The first flush diverter works to purge this first portion of likely unclean water so following rainwater is largely cleaned of pollutants that may have originated from both the atmosphere and the catchment area.
Inlet and Outlet Screens
Inlet and outlet screens are a small but fairly necessary component of a successfully operating rainwater harvesting system. Fine-mesh screens are recommended to be installed at any open-ended plumbing, such as the rainwater inflow and overflow at the storage tank.
They can be fitted to tank connections or featured along specially designed gutter channels. In order to be effective, the screens must be of a specific thickness and wire fineness. RWH screens are often made of metal such as stainless steel and corrosion proof plastic such as high-density polyethylene (HDPE) or PVC.
The use of tank inlet screens as well as pipe flap valves in rainwater harvesting is recommended as they limit and/or restrict the transfer of incoming debris and pests. Examples include debris, plant matter, animal refuse, allergens, and pests such as insects, mosquitoes, rodents, and birds.
Without protective screens, it can be possible for any material or water-seeking animal to reach the storage tank. If this occurs, it can effectively contaminate the water or lead to an infestation, and it is agreed that mosquito larva is never a desired component of any RWH system. Further, such a scenario can also promote algae and microbial growth. Collectively, without system screens the potential for resulting contamination will lead to more maintenance and cleaning of the tank. When system screens are installed, much is kept from ever reaching, and therefore contaminating, the rain tank.
Rainwater Collection Tank
Also known as a cistern, basin or rain barrel, the rainwater collection tank is perhaps the central component of a rain harvesting system. Without a storage tank, rainwater could not be collected for later use and incoming rainfall could only be diverted for distribution to an immediate application. The best rainwater cistern for an application will match and fulfill usage needs, any specific scenario requirements as well as any local law stipulations.
Rain harvesting tanks come in a variety of volume capacities, colors, and manufactured materials. The most common rain storage tanks are fabricated from high density polyethylene (HDPE) and metal rain tanks made from stainless steel and galvanized steel.
Poly rain tanks are often black to dark green in color to best negate algae growth from sunlight influences. Tanks are also available in red, yellow, brown, blue, and white for aesthetic appearance, to match visual/environmental cues, and when the specific installation will not benefit from the sunlight blocking provided by dark colored tanks. Custom color options can always be requested from select manufacturers.
Rectangular doorway or slimline rainwater tanks are another common style chosen for RWH due to their unique shape and placement ability.
In terms of water capacity, rain tanks range from small 90 to 100 gallon tanks capable of fitting almost anywhere, up to large 100,000 gallon steel tanks that require full site preparation.
When it comes to storage, it is best to choose a rain collection tank with a volume appropriate for the intended use. Select a tank that will not fill too quickly, but also don’t select one that will never get filled as cycling any sitting water is helpful to water quality.
Water Pump
Rainwater harvesting and collection systems that are integrated for use inside structural facilities or with appliances will need a water pump. Irrigation systems, sprinklers and pressurized spray nozzles will also require a water pump. A water pump will draw rainwater from the storage tank and force it throughout system plumbing, increasing pressure and flow rate. A submersible water pump is commonly used in RWH systems, especially underground water tanks.
Without a water pump, rainwater delivery becomes fully reliant on atmospheric pressure and gravity to push rainwater through water lines and out to the desired tap, fixture or appliance. In underground storage systems, this is impractical as the water tank is beneath the point of outflow and a sufficient water pump is a necessity.
Water Filter and Purification
Filtration and purification of harvested rainwater may or may not be a necessary component of a RWH system. The need and extent will depend on the rainwater’s intended use. If rainwater will only be used for lawn and garden, no treatment will likely be necessary. If a pump will be used with the rainwater, such as for appliances, irrigation and agriculture, some level of filtration may be needed to remove any hard sediments or undesirable elements. If the rainwater will be used for drinking or cooking, the greatest level of purification will be required to achieve potable (drinkable) water standards.
There are various means to purify rainwater in a storage tank. A few common examples include: ultraviolet (UV) irradiation, ozonation (administering gaseous ozone, O3, bubbled through the liquid water), chlorine and iodine treatments. Activated carbon, sediment, and/or membrane based filtration products are often used to filter rainwater.
For more info, see our Rain Tanks Series post on How to Turn Rainwater into Drinking Water.
Volume Gauge
Volume gauges are part of a healthy check and balance system. Though they may be minor and may not be required for a functional rain system, RWH tank gauges provide a significantly easier and more accurate means of monitoring the volume levels in bulk rain collection tanks rather than visual observation alone. They are especially useful in underground storage tank scenarios. Incorporating a rainwater gauge allows for a better understanding of your personal rainwater harvesting cycle of use and replenishment according to your regional precipitation patterns.
Rainwater Harvesting System Component Takeaways
Complete rainwater harvesting systems can be either very simple or complex with multiple working stages. Fundamentally, rainwater systems require just three basic components: a catchment area, a way to channel rainwater and a collection container.
Successful, modern rain harvesting systems that can provide clean, drinkable water will use several parts to progressively filter the rainwater as it moves to the tank and then from the tank to use. System accessories such as first flush diverters, filter screens, filtration units, and purification devices all work together to produce a complete RWH system that will consistently outperform less sophisticated means of harvesting rainwater.
For more info on rainwater harvesting practice, systems, and how-to guides, review our RWH blog. If looking for ANSI/NSF 61, FDA approved rainwater collection tanks, you can find them here, and rain harvesting accessories, here. If you have questions, comments or need any assistance about products or ordering, reach out to us today.