Also referred to as Rainwater Catchment or Roof Water collection, Rainwater Harvesting is used in both developed and developing countries and refers to the collection and storage of run-off rainwater for subsequent use.
The most common residential setup involves using the roof of a house as a catchment area for rain, and gutters which will then channel the run-off water into some kind of storage container.
Rainwater harvesting, while quite simple in concept, can also be very elaborate – involving many components and precise measurements in order to allow for a sustainable water system. For the purposes of this article, we'll cover the basic concepts of rainwater harvesting and how one could get started.
In this article, we'll cover:
- The advantages and practical uses of collecting rainwater
- The different methods and systems of rainwater harvesting
- All the components that make up an effective rainwater harvesting system
- Why Collect Rainwater?
- Advantages of Rainwater Harvesting
- Practical Uses of Rainwater Harvesting
- Different Methods and Systems of Rainwater Harvesting
- Components of a Rainwater Harvesting System
Why Collect Rainwater?
Rainwater harvesting has gained particular popularity in developing countries where water scarcity is prominent, making rain one of the major sources of water for many. And while it remains a major source of water for those regions, it continues to be a popular method of water collection for residents and businesses in developing countries such as Germany, Singapore, Australia, Japan, China, and the United States.
Why then are more and more households and businesses relying on rainwater as an alternative source of water?
- In regions with adequate rainfall, rainwater harvesting creates water independence and self-sufficiency
- In almost all cases, rainwater is a free source of water
- Because of its lack of chlorine, rainwater is ideal for landscape gardens and plants.
- Rainwater harvesting also helps in reducing runoffs and solving drainage problems while giving you unrestricted access to free and clean water.
- It can act as an excellent backup source of water
- Easy maintenance
1" of rain x 1 sq. foot = 0.623 gallons
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Advantages of Rainwater Harvesting
The collection and numerous uses of rainwater come with a host of benefits. Some of these benefits are discussed below.
It Acts as a Backup Water Source
Water supply systems each have their uncertainties and sporadically need repair and maintenance. Also, droughts may cause water shortages. Such major repairs or periods of drought may result in the unavailability of water for daily use. However, a well-built and proper RWH system in place will allow you access to an alternative source of water for other household/business purposes while saving the little potable water for drinking and cooking.
Probably one of the most important benefits of rainwater harvesting is the role it plays in the fight against water scarcity. It is estimated that about 35% of water at home is used to flush the toilet. When you add that to the amount of water you use to water your plants, garden, lawn, and wash cars, you see the amount of clean and potable water being wasted. RWH can help you greatly reduce the amount of safe water used in performing these chores. This reduction in the use of potable water will, in turn, reduce the amount of water being pumped from groudnwater sources which will, in turn, reduce the chances of drying up these water bodies.
Low Initial Capital, Reduced Utility Costs, and Easy Maintenance
Due to its relatively simple components, the installation of an RWH system does not require a lot of capital. And the extra water source provided by the rainwater harvesting system will eventually bring down overall water costs. With very low maintenance costs, the entire rainwater harvesting application is not only cost-effective but can save money in the long-term.
Helps in Reducing Flooding and Erosion
Most RWH systems used to provide water to buildings feature built-in catchment areas around the rooftop which usually are capable of collecting and storing huge amounts of water. By collecting this water, flooding and soil erosion are greatly reduced since there is a reduction in the flow of water.
Practical Uses of Rainwater Harvesting
Farming and landscaping are two activities that use up enormous amounts of water. Rainwater harvesting provides a less costly and more eco-friendly source of water for these activities. Rainwater is ideal for farming especially because of the absence of chlorine or any other chemicals which may prove harmful to plants and animals. It can also offer an alternative source of water for the watering of lawns, plants, gardens, and filling up of swimming pools.
In-Home Use - Drinking/Cooking
With the proper purification systems installed, rainwater harvesting can also be a source of water for cooking and drinking.
Finally, it can also be used to protect against fires. This is especially the case in regions suffering from water scarcity or in areas not connected to the main water supply. This can be done by installing fire plugs which are innovative fire protection devices that automatically fill roof gutters with water in the event of a bushfire threat. In Fort Davis, TX, rainwater runoff is stored for fire safety purposes by the McDonald Observatory.
Different Methods and Systems of Rainwater Harvesting
This technique features a large container usually located a few meters from the property. The roof gutter is channeled into the storage tank. This system is referred to as the “dry” system because, after rainfall, the pipes get dry since all the water empties into the top of the tank.
Advantages of this method include larger storage preventing flooding in case of heavy rainfall and easy implementation and inexpensive to install. This system is especially ideal for stormy areas.
While the pipes channeling water in the dry system are located on top of the storage tank, the pipes here are located underground and beneath the storage tank causing the pipes to continually be full of water, hence the name “wet” system. With this method, a number of pipes are connected to multiple plugs on the building and channeled underground into an empty storage tank. In the absence of rainfall, the water level remains constant with the pipes constantly full of water.
However, because the pipes are always full of water, it is advised that pipes be watertight to avoid leakage into the soil. This method is the most expensive of all three systems due to underground piping.
The rain barrel is probably the easiest and cheapest RWH system and is widely used by households. This system involves the installation of a barrel underneath the roof drain pipe such that all the rain falling on the roof will be guttered and funneled into the barrel. The barrel usually features a plug at the bottom which makes it possible for water to be drawn or for a hose to be connected.
One major advantage of this method is the ease of use. Barrels can easily be purchased or sourced whether new or recycled. If you choose to use a recycled barrel, it would be prudent for you to know what the barrel was formerly used for to be sure there are no chemical residues left. Also, find a lid for your barrel if you live in a mosquito-infested area.
Components of a Rainwater Harvesting System
For most RWH systems, this is usually the roof of a home. But any flat surface with a downward angle can act as the catchment area. It is important to take a number of factors into consideration when building a rainwater harvesting system:
- Most roof material for the catchment area. However, if you plan to build your system from scratch, a metal roof is the best material to use because water slides down immediately, avoiding the risk of bacterial festering. Wood surfaces and materials that contain lead might require that the water be purified before use, especially if being considered for consumption.
- Another factor is the slope of the roof as it determines how quickly water will drain to gutters during rainfall. Steep roofs cause water to run off quickly making it easier to clean the roof and prevent contamination. Less-steep roofs, on the other hand, reduce runoff making it more possible for contamination to remain on the roof.
- Size is important as it will determine the amount of rainwater harvested. Knowing the area of your catchment area can help you determine how much water you can harvest. The area can be calculated by adding the building’s area to the area of the roof’s overhang. The larger the size, the greater the volume of water harvested.
Use this formula to determine the amount of water that can potentially be collected: 1" of rain x 1 sq. foot = 0.623 gallons
This simply refers to the components that will transfer water from the catchment area to the collection area, typically gutters and drain pipes. Consider the following when selecting gutters and drain pipes:
- The size of the gutters should allow adequate movement of rainwater harvested from a storm event. Thus, storm-prone places require wider gutters than places with less-intense rainfall. Gutters should generally be at least 5 inches wide.
- Every 100 sq. foot of catchment area should have one inch of drain pipe. The same rule should be applied to circular PVC piping.
- It is important to properly install drainpipes and gutters for the system to function properly.
- For effective draining, gutters should be sloped at 1/16” per foot of length.
- Also, rounded-bottom gutters reduce the risk of debris buildup.
- Also, consider putting gutter hangers after every 3 ft. In areas with heavy snow, gutters should be placed after every foot.
- Paint PVC pipes to minimize UV sunlight breakdown.
This is where the collected rainwater is stored for subsequent use. Some things to consider include:
- It is important to make sure that the observation port is inaccessible to anyone to prevent accidents and unfortunate incidents.
- Also, it is important to carefully select the material for your storage tank. Ideal storage tanks include are either enclosed metal or polyethylene plastic to reduce mold growth.
- Also, the color of the tank is very important as it plays a number of roles. First, it preserves the quality of the water. Clear (translucent) tanks encourage the growth of algae since sunlight can penetrate the material. It is therefore important for clear tanks to be painted. Also, tank color can affect the temperature of the water. During summer, water in tanks with lighter colors tends to be colder since the color reflects solar energy. Remember that the container still needs to be opaque. The best way to increase solar reflection and opaqueness is to paint a black storage container white.
- It is also important to take into consideration the location of your tank – whether it will be underground or aboveground. While below-ground tanks take up less space, are less visible, and maintain a constant temperature all year round, they are prone to cracks due to soil shifting and settling. Also, they are constantly open to water pollution and cracks can be very difficult to detect. Below-ground storage tanks are also costlier to install, remove and maintain. Aboveground storage tanks are subject to weather conditions including sunlight, and this may affect the water quality.
Treatment is a very important part of the system as it makes the water harvested safe for use. During harvesting, water can be contaminated by microbiological organisms, chemicals, and debris. Microbiological organisms include viruses, bacteria, and parasites. Chemicals include synthetic organic chemicals (SOCs), volatile organic chemicals (VOCs) and other metals.
- To avoid chemical contamination, it is important to avoid roof materials and gutters that contain lead or copper.
- To avoid contamination by debris, consider installing debris-screening filters. This should be installed in the gutter to filter out leaves and other debris from making their way into the system. Screening filters should also be placed in the drainpipe to filter out debris draining from the gutter. Finally, one should be placed in the inlet into the storage container.
- Once the water has been stored, the treatment of the water will depend on its intended use. If the water is meant for irrigation, then the water may not need any extra treatment. However, if the water is intended for indoor use, consider using different water filtration techniques to maximize effectiveness and eliminate chemical and microbiological contaminations. This can include one or all of the following techniques: chlorination, UV light, ozonation, disinfection, and absorption.
It is important to note that friction in the pipes will lead to a loss of pressure. This is especially true if you plan to move the water far from your storage tank. Consider calculating friction loss using the Hazen-Williams Friction Loss Equation.
Pressure tanks and Pumps are optional components of a distribution system. If your RWH system uses gravity flow, there is no need for a pump. However, it is important to note that selecting the perfect pump for your system will depend on your volume and pressure requirements. Pressure tanks make sure a certain volume of water is pressure-stored.
Rainwater is a source that if harnessed correctly, can provide a system of sustainable water to those where water isn't always readily available. It allows for full control of your own water supply for agricultural, home, and livestock purposes. The dry, wet, and barrel systems have different methods of capturing rain, but all include similar components: catchment, conveyance, storage, treatment, and distribution. Let's continue to educate each other on rainwater harvesting as a viable means of combating the global water crisis.
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