In the guide below, we outline various key aspects of rainwater harvesting and collection.
We discuss what it is, the different methods & systems, how rainwater might be used, examples of regions and countries that use it, regulations, and more.
What is Rainwater Harvesting & Collection? (A Definition)
A general definition of rainwater harvesting and collection might be:
The collection/harvesting of rainwater specifically from a roof type surface, which is then stored in a rainwater storage setup for later use
The Difference Between Rainwater & Stormwater
The main difference between rainwater and stormwater might be …
Rainwater is collected specifically from a roof type surface, without it hitting the ground and becoming runoff
Stormwater on the other hand is generally water that falls on ground surfaces like roads and drains, and does become runoff
Some reports indicate that rainwater might be a cleaner type of water than stormwater
Rainwater may sometimes only needs simple filtration or disinfection processes because it might be low in salinity, and free from bacteria or suspended matter that other types of water might not be (but, it depends on the rainwater, and where and how it’s collected)
How Rainwater Collection & Harvesting Works
There might be three general components or stages to rainwater collection and harvesting:
1. Rain water falls onto a roof type surface, which essentially acts as a catchment area
2. Rain water is transferred from the roof catchment area via gutters and pipes, or some other type of transfer system or rainwater collection points
3. Rain water arrives in the allocated storage area (such as a tank)
Different Types, Methods & Systems Of Rainwater Harvesting & Collection
There’s a range of different types, methods and systems of rainwater harvesting and collection that can be used.
Potential Categories Of Rainwater Harvesting & Collection Systems
– Simple vs Advanced Systems
– Gravity Systems vs Systems That Use Energy (e.g. pump fed systems)
– Automated vs Non Automated Systems
Other Ways To Differentiate Rainwater Harvesting Systems
Systems might be differentiated by:
– How they catch water (e.g. from a roof, or directly into a catchment area of the storage equipment)
– The water transfer system used, and whether it’s pumped/pressurised or not
– The type of storage used, and where it’s located
– Plus, other miscellaneous features of the system
Different Types Of Rainwater Harvesting & Collection Systems
The most common type of rainwater harvesting and collection system might be a rainwater storage tank (or multiple tanks), which receives water from pipes connected to a roof catchment area with either designated collections points, or a gutter with downpipes.
Tanks are usually above ground, but can also be installed below ground.
Water butts are another form of a tank used in some countries.
Other Rainwater Harvesting & Collection Systems
Other systems that can be used might include:
– Ponds (in the case of plastic ponds)
– Freestanding tanks and patented products that catch water directly from the sky without a roof surface
Cisterns may be different to other systems because they allow water to fall to the ground
wikipedia.org notes that cistern methods and systems involve: ‘… pumping the rainwater that has already soaked into the ground or captured in reservoirs and storing it in tanks (cisterns)’
Different Features Used On Different Rainwater Harvesting & Collection Systems
Some of the different features used on different systems might include:
– More advanced systems may involve pressurisation, pumps, and treatment devices such as UV lights, chlorination devices and post-filtration equipment
– Some systems use solar panels in some capacity for rainwater collection, either as a catchment surface, or for solar disinfection
Storing Rainwater Naturally
There may also be ways to store rainwater naturally.
wikipedia.org notes that: ‘[Rainwater harvesting is possible by growing freshwater flooded forests]’
What About Detention Basins & Retention Basins – Are They Forms Of Rainwater Collection/Harvesting?
– Detention basins and ponds are made primarily for the purpose of protecting an area against flooding or erosion. Therefore, they may not be considered a form of rainwater collection
– Retention basins and ponds are similar, in that they might be made to protect against flooding and erosion, whilst also managing stormwater runoff, and improving the water quality of nearby sources of water
Different Uses For Rainwater
What rainwater is used for depends on where it’s collected, by who, and what the law is in a given area.
But, the main uses may be potable water, and non potable water.
In some regions of the world, drinking/consumption of rainwater is allowed by law.
Rainwater equipment may be set up with a filter, or the water might be treated, filtered, purified, or disinfected in some way before being consumed.
In some regions of the world though, the consumption of rainwater from a private supply may not be allowed.
Apart from drinking rainwater, some of the other potential uses of rainwater may include:
– Domestic use, such as for washing, cleaning, cooking, watering, flushing toilets, and so on
– Agriculture, and specifically irrigation. Some farms may collect rainwater on-site for irrigation
– Different commercial and industrial uses
– Some rainwater overflow is used for groundwater recharge
Some rainwater runoff can also be redirected to aquifers as a form of groundwater recharge and replenishment. washmatters.wateraid.org notes that apart from natural replenishment of aquifers via rainwater runoff via percolation: ‘Artificial recharge to [an] aquifer is the process of draining the rain water or surface water into the aquifer by constructing simple civil structures’
Different Levels & Scales Of Rainwater Harvesting & Collection
Rainwater can be harvested on a smaller level, like for example at individual households.
However, rainwater can be harvested at larger levels too, such as commercially or industrially by companies, farms, public groups like schools and even hospitals, and so on.
renewableenergyhub.co.uk discusses commercial and industrial rainwater collection in more detail
Rainwater As A Form Of Self Supply & Private Supply
Collecting/harvesting rainwater is seen as a form of self supply or private supply, because it’s water that is collected by a private entity, and separate to the public water supply (from the public water supply network and public pipes).
However, some groups such as businesses may collect rainwater privately, but use it for products or services that are served to the public.
Different regions have different regulations relating to private rainwater supplies being used as a part of a service to the public.
Countries & Regions That Collect Or Harvest Rainwater
A range of countries and regions collect or harvest rainwater across the world, using different systems and methods of collection.
South Asia, and in particular Thailand for example has in the millions of tanks installed at private household for self supply of rainwater
Frankfurt Airport may currently have the biggest rainwater harvesting system in Germany
wikipedia.org gives examples of various countries currently using rainwater collection and harvesting to different extents around the world, such as Kenya, Australia, India, Canada, the UK, the US, Uganda, Thailand, Bermuda, New Zealand, and Sri Lanka
Legislation, Regulations & Guidelines On Collecting Rainwater, & Drinking Or Using It
Different Regions Have Different Legislation, Regulations & Guidelines Relating To Rainwater Collection, & Consumption Or Use
Different countries and regions around the world have different legislation, regulations and guidelines relating to the collection and consumption or use of rainwater, such as:
– Whether the collection of rainwater is allowed
– The conditions of rainwater collection
– What rainwater can be used for (potable or non potable uses)
An Example Of The Regulation Of The Consumption Of Rainwater
Specifically when it comes to the regulation of drinking or consuming rainwater, one example of how it’s regulated in one part of Australia is:
– South Australia
South Australia’s ‘Safe Drinking Water Act’ currently does not apply to domestic use of rainwater tanks or other private supplies, but does apply to drinking water providers who supply water to the public.
Other Regulations On The Collection & Use Of Rainwater
Promotion Of Rainwater Use By Some Regions
Some regions or countries outright promote rainwater use.
As a few examples:
– Oklahoma in the US previously passed the ‘Water For 2060 Act’ to promote rainwater and graywater use
– Sri Lanka passed the ‘Urban Development Authority (Amendment) Act, No. 36 to promote rainwater harvesting, and also has an initiative set up for rainwater harvesting
– According to rainwaterharvesting.org, some cities like Chennai, Bangalore and Delhi have made rainwater harvesting part of State policy, and practice it on a large scale.
Collecting & Harvesting Rainwater In The United States
In the US it’s the same – different States in the US have different regulations and guidelines around whether rainwater harvesting is allowed, and the conditions under how it’s to be done, and what the rainwater can be used for.
Colorado used to almost completely restrict it, but now some residential owners who meet certain criteria may be able to obtain a permit to install certain rainwater collection system
On the other end of the spectrum, parts of New Mexico may make it mandatory in new dwellings, and Texas may offer a sales tax exemption for rainwater harvesting equipment
Texas and Ohio are two examples of States that may specifically allow rainwater collection specifically for potable purposes
Quality Of Rainwater, & Treating Rainwater
Rainwater may be filtered or treated in several ways before being consumed or used (known as pre-filtration, or pre-treatment). Some of those filtering or treatment methods might include:
– A basic filter of some type, such as a sediment filter
– A more advanced filter like a self cleaning filter which is installed inside the storage tank
– Boiling rainwater via solar water disinfection with solar powered cookers/boilers (this is seen as a low cost way of treating the water)
– More advanced water treatment might involve a high intensity UV sterilizer to make the water suitable for drinking, or some other type of advanced water treatment
New Research On Potential Safety Risks of Rainwater Harvesting & Collection
euronews.com identifies that (paraphrased) at least one new piece of research indicates that rainwater in most locations on Earth contains PFAS substances (also called ‘forever chemicals’), which are human made chemicals that don’t ever break down in the environment.
Some scientists indicate that there could be a risk in being exposed to these substances
There may be a ’cause and effect’ risk of being exposed to these substances, and having an increased risk of certain health issues
However, others indicate this might not be the case.
Potential Pros & Cons Of Rainwater Harvesting & Collection
1. Various ‘Better Meets Reality’ guides
5. https://washmatters.wateraid.org/publications/rainwater-harvesting-for-recharging-shallow-groundwater-2011, via their PDF document