Guide to Rainwater Harvesting Systems
This guide covering the use of rainwater harvesting systems has been developed by the resource optimisation and water reuse specialists at Water Treatment Services. It reviews a number of the most common rain water collection systems used in both domestic and commercial environments. The guide looks at the benefits that can come from the reuse of rainwater, how and where it can be used, and describes the different types of commercially available harvesting systems and how they work.
Why install a rainwater harvesting system?
Over the last couple of decades we’ve all become a lot more aware of the natural resources we use and how our actions impact the environment around us.
Both businesses and private individuals have done lots to reduce their environmental impact, and save money too.
We’ve begun to recycle our waste, we’ve installed solar panels on roofs, improved insulation in buildings, installed double glazing, switched to low energy lighting and tried to reduce our overall energy consumption.
One of the ways of saving money, lowering our impact on the environment and reusing natural resources that is often highlighted is the introduction of a rainwater harvesting system to allow water reuse… but what exactly is this and how do you go about it?
What is rainwater harvesting?
A rainwater harvesting system is a physical system which collects rainwater that falls on to buildings, other structures, carparks and hardstanding areas, which would have ordinarily flowed down the drain.
As rainwater falls on to a roof or other external surface it is directed into guttering or gullies in the normal way.
However, the difference when using a rainwater harvesting system is that the water is then diverted into storage tanks for later reuse, with or without treatment.
Typically, people in the UK use around 150 litres of water per person, per day
All sorts of rainwater harvesting systems are now available, from small scale systems suitable for a domestic use to much bigger commercial systems designed to cope with larger volumes of water from office buildings, factories, hospitals, schools etc.
What’s the difference between rainwater and greywater?
It is important not to confuse rainwater with greywater.
Grey water is the term used to describe water from washing machines, baths, sinks or other similar appliances.
Uses for greywater recycling are more limited as it is often more heavily contaminated with soap and other potential pollutants.
What can harvested rainwater be used for?
Water harvested from a roof will not have been treated and will not be suitable for drinking.
However, there are a number of other ways in which harvested rainwater can be re-used in domestic and commercial settings.
Some of the most common ways in which harvested rainwater can be reused include:
What are the advantages of using harvested rainwater?
Typically, people in the UK use around 150 litres of water per person, per day.
Only a tiny percentage of this water is used for drinking and needs to be treated to make if potable quality.
Potable water, also known as drinking water, is water that is safe to drink or to use for food preparation.
The water which we use to flush toilets or to water the lawn doesn’t need to be treated to the same high standards as drinking (potable) water, but it is all processed and pumped to our homes in the same way.
A rainwater harvesting system could help to reduce water and wastewater bills considerably in both domestic and commercial settings.
What are the different types of rainwater harvesting system?
The type of rainwater harvesting system you opt for will depend on a number of factors.
The size of the water storage tank will be determined by the number of people in the home, and how you plan on using the water.
For example, a 1500 litre storage tank should be sufficient for a small home occupied by two people.
If however you are running a commercial business with more staff, or need water for agricultural purposes or a market garden, a tank of 15,000 litres or more may be required.
Common types of rainwater harvesting and water reuse systems include:
Water butts
The common water butt is the most basic form of rainwater harvesting, and might meet the needs of some domestic users perfectly.
When it rains water flows down the guttering from the roof and straight into the water butt.
The butt can then be used to supply water for watering plants or lawns in the garden.
Domestic customers who are billed for their water use through a meter and who switch to using a water butt should immediately see a reduction in their water bills.
If the water butt is fitted with a filter, this can also greatly improve the quality of the rainwater collected.
Direct pumped submersible rainwater harvesting systems
Direct pumped reuse systems are perhaps the most common type of rainwater harvesting system in domestic properties after the water butt.
The main advantage of a direct pumped system is it’s easy to install.
Water flows off the roof and into the guttering in the same way, it is then diverted into a rainwater storage tank.
Tanks are generally located close to the property but can be buried underground and so completely hidden.
The pump is located inside the water tank, and the harvested rainwater can then be pumped into the toilet cistern, washing machine or other appliances when it is needed.
If there is a particularly dry spell and the water tank runs low, mains water can be used to top it up.
This type of system can also be used in commercial settings, usually with a larger storage tank and two or more pumps rather than one.
Direct pumped suction systems
Pumped suction systems are similar to the submersible system with one important difference.
The pump used to distribute the water around the property is not inside the rainwater tank itself.
Instead, installers will put the pump on a control unit panel somewhere inside the property such as a kitchen or utility room.
If the rainwater tank runs dry, there is no need to top it up from the mains as the control unit will simply detect that the tank is empty and will automatically switch to mains supply until there is harvested rainwater available again.
Indirect gravity collection systems
An indirect gravity system is a slightly more complex type of system in that involves two water storage tanks, not one.
Rainwater is harvested in the same way and then stored in the same type of large rainwater storage tank.
However, it is then pumped into a storage header tank, usually located in an attic or a loft.
When you turn the tap on, or use a washing machine, gravity forces the water down.
If there is no water to fill up the header tank, it is replenished directly from the mains supply.
Indirect pumped systems
Again, an indirect pumped system is similar to the gravity system in that it uses two separate tanks, one to store the water when harvested and another to supply the water when needed.
However, as this system uses a pump and not the force of gravity to get the water to where it is needed, the second tank can be located anywhere in the building.
This is one of the most flexible types of system as pumps can be set to provide the perfect flow and pressure required for the building’s needs.
Gravity only rainwater systems
A gravity system is one of the most simple, but is also only suitable in a very small number of cases.
In order for a gravity only system to work properly, the storage tank must be below the level of the roof and the gutters, and also above all outlets which are going to use the harvested rainwater.
As there are no pumps involved it’s a reliable system with no moving parts to fail, and an exceptionally eco-friendly, energy efficient choice if the architecture of the building makes it possible.
Do you need to treat rainwater?
On all types of water harvesting system, even the standard water butt, there is the option to add in filters to purify the water collected.
This will not bring it up to the standards required of drinking water, but will filter out dirt, twigs, moss and other debris which could clog up the system.
Disinfecting the water should also be considered to control bacteria and other waterborne pathogens that may contaminate the water.
There are ways of purifying water collected from the roof to the high standards required of drinking water, but this is usually cost-prohibitive when mains water is available.
How to choose a rainwater harvesting system?
It is impossible to say which method of harvesting, storing and using rainwater is best or worst for you.
The decision on which system to install will depend on a number of factors including cost, the size and use of the building, and any restrictions in the building concerned.
For example, if there is limited or no attic space, then any system based on a header tank might automatically be ruled out.
If you don’t require water at a specific pressure, many users opt for the indirect gravity option and the high level header tank.
For commercial buildings, or when users need to have water delivered at a set pressure, it’s usually best to opt for an indirect pumped system.
There is a lot to think about, so get the experts in to discuss the options, installation costs and potential savings on bills.
Specialist water re-use and resource optimisation solutions
Water Treatment Services offer a comprehensive range of innovative resource optimisation and water re-use solutions including the design and installation of rainwater harvesting systems that can save on valuable resources, improve environmental performance, and reduce both water and wastewater costs.
Our experts can provide advice and support to help you identify the most appropriate water re-use strategies for your buildings and facilities.
With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained engineers and equipment specialists we offer cost effective engineering and environmental support solutions across the whole of the UK and internationally.
Contact us today to learn how our rainwater harvesting and water reuse solutions can help you and the environment.
Further reading…
More information about about water re-use and resource optimisation
REVIEWS
Read our reviews
