Quick Key Facts
- Water harvesting is the practice of collecting and storing water from rain, stormwater runoff, gray water, snow, air and fog. Its use includes nonpotable purposes such as irrigation, flushing toilets, laundry and recharging groundwater supplies, and potable use such as drinking water.
- As water scarcity is an issue for densely populated regions, rainwater harvesting can supply water for use by businesses and households in dry seasons, as well as create less of a demand on municipal water supplies — much of which pulls from distant areas, typically affecting those communities and ecosystems.
- Since rainwater collects dust and pollutants through the atmosphere, and collects contaminants where it lands on the surface, rainwater collected from unclean surface runoffs isn’t suitable for drinking water and needs to be purified.
- Water treatment processes such as flocculation, settlement and biofilm skimming can be used to get rid of bacteria, organic material and chemicals. Prefiltered water can also undergo solar water disinfection (which uses solar energy) or be treated with chlorine.
- Although many areas around the world encourage and subsdize rain barrels and other rainwater harvesting systems, some areas in the United States view it as a water rights issue, and place restrictions on the practice.
- Rainwater harvesting can also be used to recharge groundwater supplies, which sometimes can get so low that wells go dry.
- Water can also be harvested from air using technology called an Atmospheric Water Generator, which pulls moisture from the air like a dehumidifier does and can be used to create potable water — something that could be beneficial during shortages, contamination events, natural disasters and other issues that interrupt availability of drinking water.
What Is Water Harvesting?
Water harvesting involves the harvesting of rainwater, or water from the atmosphere through systems that involve collecting it for drinking and irrigation.
Rainwater harvesting is thousands of years old, and on a smaller practical scale, rainwater is a good way to conserve water for later use, particularly during dry seasons, and also saves money from using municipal water sources while protecting groundwater supply.
On a larger scale, it provides water for areas and communities dealing with water scarcity. Currently, areas all over the world are increasingly experiencing droughts. In 2022, 73% of the Western United States alone was in severe drought classification, while 31% was in extreme drought.
According to the United Nations World Water Development Report, 2 billion people globally also don’t have access to clean and safe drinking water, and scientists estimate that 4 billion people live in regions with severe fresh water shortages for at least one month each year, which may rise to between 4.8 billion and 5.7 billion by 2050 for reasons that include climate change, polluted water supplies and increased demand due to population growth.
Usage of rainwater harvesting has been increasing steadily. According to the global market, in 2020 $6 billion was spent on rainwater harvesting systems and is projected to increase by 4% by 2027.
Building systems can be simple or elaborate. This article will discuss rainwater catchment around the world, and how you can make it happen in your own backyard.
History of Rainwater Harvesting
Waterproof cisterns thousands of years old are evidence of rainwater harvesting, for household use as well as dryland farming, in Asia, the Roman Empire and areas of the Middle East.
In India, archeological evidence of water conservation and harvesting was deeply rooted in the science of ancient India with many systems differing in its various regions to adapt to its uniqueness — some of which are still in use today.
One of the methods involved taankas. First built in the year 1607, they are a traditional rainwater harvesting method that involved an underground cistern that could store water for dry seasons to give to individual households or the community, or use for livestock. They vary in size and could hold anywhere from 1000 liters to 500,000 liters of water.
Indigenous cultures in the U.S. also created trenches that brought water naturally down from the mountain to the villages for drinking, crop irrigation and livestock.
Early settlers in North America also collected rainwater in barrels to do laundry and bathing. The water that was collected was more appreciated for its softness, and it was during this era that the phrase “hard water” would come about, which was groundwater and surface waters whose mineral content was too high to use.
Rainwater harvesting in some areas lost favor for awhile, but gained traction again in the 1950s, particularly in Australia, where roaded catchments were constructed to collect water for agricultural purposes.
Interest in research for water catchment for livestock also surged around this time in the U.S., and later in the 70s and 80s, for crop purposes in Africa.
Rainwater Harvesting and the Environment
There are several environmental benefits of rainwater harvesting.
Reducing Energy Use and Carbon Emissions
When wastewater flows through sewer systems, it requires a lot of energy at treatment plants before being pumped back through the system into local waterways where it’s used again for any number of purposes, such as drinking water, irrigating crops and sustaining aquatic life.
The energy used to do this involves fossil fuels. Wastewater treatment plants may be responsible for emitting up to 23 percent more greenhouse gases because of fossil fuels used to treat detergent-laden water from residential showers, household washing machines and industrial sites. So when you harvest and use rainwater, you’re helping to save energy and reduce carbon emissions.
Replenishing Groundwater Supplies
Collecting rainwater for use in the garden will allow you to release it into your garden later when the ground is not saturated, to recharge groundwater supplies to continue to hydrate the soil.
Creating Healthier Soil and Plants
Rainwater is great for plants, because it’s free of chemicals and salts that are in treated water, and can alter the chemical composition of the soil (and also end up with what you consume when you eat plants). Rainwater also has a balanced pH that is required by plants.
Reducing Runoff
Collecting rainwater reduces the amount of runoff water that collects pesticides and other chemicals, and relieves sewer systems, which could overflow in areas that cannot handle the volume of runoff, which helps avoid contamination of the ground.
Reducing the Overdrawing of Groundwater
Water reservoirs and groundwater are usually overdrawn, particular in urban areas where there isn’t as much surface area to absorb water.
Where Can Rainwater Harvesting Be Used?
Rainwater harvesting can have a number of applications and can be from simple to elaborate.
A simple rainwater harvesting system where pipes run from rain gutters into a rain barrel or tank is known as a “dry system” because they don’t hold any water in the pipes after rain ceases. They also do not create breeding grounds for insects.
“Wet Systems” are used when pipes can’t run directly into tanks, which may be located far away from the collection surface, or where a series of tanks services a number of areas. These systems, where pipes go underground, can utilize a pressurized system to avoid retaining stagnant water, and can be mosquito-proofed through screens and filters.
Since rainwater collects dust and pollutants through the atmosphere, and collects contaminants where it lands on the surface, rainwater collected from unclean surface runoffs isn’t suitable for drinking water and needs to be purified.
Domestic Use
As mentioned above, throughout history rainwater harvesting has been used by households for drinking water, watering the garden, laundry and other uses.
Residential rain collection can be caught from the roof or the ground. Roof catchment systems collect water from its surface and route it through a system of gutters and pipes into a rain barrel, usually located on the ground level.
Choice of roofing material for this is important since some types of material, like those with coatings or metallic finishes or asphalt, could contaminate water. It’s better to use aluminum, tiles, slate or corrugated iron roofs.
A ground residential rainwater collection system collects water via drain pipes or earthen dams and stored above or below ground in tanks. The quality of water may be lower at the ground level, rendering the captured water suitable for landscaping needs only.
Costs for systems can vary. An inexpensive DIY system could run around $200 with a 55-gallon barrel, or up to $20,000 for a more complex roof catchment.
Agricultural Use
Rainwater harvesting is a great way to sustainably irrigate crop fields. It also serves as a form of damage control by diverting heavy rainfall from damaging crops.
Urban Areas
As America’s cities struggle with water supply shortages and runoff pollution problems, capturing rainwater from rooftops provides a solution to increase water supply and improve water quality, according to a recent analysis on “Capturing Rainwater from Rooftops” by the Natural Resources Defense Council (NRDC).
Using rainwater catchment in urban areas also reduces one’s dependence on municipal water, which is the tap that gets treated and rerouted through pipes underground to your faucet. This lowers bills, and also reduces the carbon footprint used by the water treatment facilities before it reaches your home or business.
Some places in cities use blue roof systems which detain stormwater to mitigate flooding.
Commercial Rainwater Catchment Systems
Large-scale rainwater catchment systems on buildings can lower utility costs and provide water for flushing toilets, irrigation for landscaping, fire suppression, manufacturing processes, vehicle washes, laundries and filling pools.
Rainwater Harvesting Limitations and Disadvantages
Rainfall is not always dependable, particularly in arid regions that undergo long drought and dry seasons.
It requires regular maintenance as systems are prone to rodents, mosquitoes, algae growth, insects and lizards which can contaminate the harvested rainwater.
Setup costs for the rainwater harvesting system are high.
Global Water Harvesting Initiatives
Several initiatives around the world utilize rainwater harvesting to provide water for communities in need.
One of them is the Global Rainwater Harvesting Collective, a project of the UN’s Department of Economic and Social Affairs. It helps provide drinking water to schools facing shortages and utilizes rooftop catchment systems on schools.
In India, NGO One Prosper provides families with filters and water harvesting systems in the Thar Desert, where many people, particularly young girls, spend up to seven hours a day trying to retrieve water from far outside of town to bring back for use, which detracts from their education. They also provide families with seeds and farm training so they can grow their own food, and build farming dykes so they can leverage rainwater to irrigate and double crop yields for those who grow millet for income.
California-based Save the Rain also provides systems at homes and at schools on several different continents where water scarcity is an issue, particularly in Tanzania. To date they have installed systems on 4710 homes, and at 365 schools. The group said that 80% of children were walking for water instead of going to school, but with these systems, schools retain up to 95% retention rates.
There are also several initiatives in Mexico such as Isla Urbana, which installs systems in communities that lack access to water.
Founded in Texas in 1994, the American Rainwater Catchment Systems Association was created to renew attention to rainwater harvesting, and whose goal is to promote a favorable regulatory atmosphere, creating a resource pool and educating professionals and the general public regarding safe rainwater design, installation and maintenance practices.
Atmospheric Water Harvesting
Much like a household dehumidifier can pull moisture from air to keep things from getting moldy, the same process can pull water from the atmosphere to create potable water.
While the market is relatively small right now, the technology has been around for decades. Several companies have sold and sent devices to drought-stricken regions for disaster relief and to replace contaminated drinking water.
While there are larger for-profit enterprises, one of the more grassroots is public charity the Moses West Foundation which has been providing atmospheric water generators during crises like in Flint and Mississippi and other disenfranchised areas with water issues. Since the foundation’s inception they’ve provided 4.5 million liters of clean water.
Much of the technology that’s used differs from dehumidifiers in that water quality controls are built into the machine.
Another atmospheric water harvesting technology, hydropanels, utilizes desiccants, which are materials that soak up moisture (some are found in silica gel and baby nappies).
California-based company Water Harvesting is also developing devices that range from small kitchen countertop harvester for households to large scale industrial use for village communities.
Swedish company Drupps has built machines that harvest water from waste steam from industrial chimneys and turns it into drinkable water. According to their website, their process uses latent heat from the steam to power atmospheric water generation, while reducing energy use and carbon dioxide emissions in drying processes.
Another angle of this technology, fog harvesters, have been around for decades in regions subject to water scarcity and fog. The process uses vertical mesh nets to induce the fog-droplets to fall down into a trough.
Policies and Incentives
Globally, policies and incentives have grown over the years to mandate rainwater harvesting systems.
India has seen many mandates and reforms with rainwater harvesting systems. In New Delhi, the Ministry of Urban Development has made rainwater harvesting mandatory in all new buildings with a roof area of more than 100 square meters and in all plots with an area of more than 1000 square meters that are being developed.
The Central Ground Water Authority (CGWA) has made rainwater harvesting mandatory in all institutions and residential colonies in notified areas (South and South-west Delhi and adjoining areas such as Faridabad, Gurgaon and Ghaziabad). This is also applicable to all the buildings in notified areas that have tube wells. CGWA has also banned drilling of tube wells in notified areas.
Tamil Nadu also became the first Indian state to make the practice mandatory in every building, to avoid groundwater depletion.
The governments of Cambodia, Haiti, China, Thailand and Brazil have all deployed rainwater harvesting systems for households and industries.
In 2003, a public-private partnership called “1 Million Cisterns” in Brazil aimed at providing 1 million households located in drought-prone parts of the South American country with easy-to-access harvested rainwater. So far the program has benefited 628,355 families.
United States
In the U.S., the top five states for rainwater harvesting with government incentives and rebates are Texas, California, Arizona, Iowa and Illinois.
Various regulations include some states requiring permits and code compliance, limiting how much water is captured, and requiring nonpotable usage only.
Colorado had a longtime ban on home rainwater harvesting over the concern that household rain barrels would take water from the supply available to agriculture and other water rights holders. That ban was lifted in 2016, but now there are other strong regulations.
A guide to regulations by state can be found here.
Takewaway
There are many environmental and health benefits to water harvesting, especially as a means to provide water to communities affected by water scarcity, water contamination and/or natural disasters. While there are some drawbacks, particularly with the cost of installation, several governments and private agencies offer incentives to help install systems.
In some areas of the world, initiatives are not only providing rainwater harvesting systems, but also using them as a starting point to revive and empower communities through more jobs and food security.
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