Frequently asked questions

What is Rainwater Harvesting?

Rainwater harvesting is a way of saving the rainwater which would normally flow off a roof and down the drain, and using it as piped water to flush toilets and for the garden watering, patio cleaning, vehicle and car washing, instead of treated drinking (potable) water.

How does rainwater harvesting work?

A storage tank is fitted to your downpipe from your roof, and falling rain enters the tank through a filter which removes leaves and other matter. The storage tank is usually buried under car or vehicle parking, a garden or under the entrance access or drive, and contains a pump which pumps the rainwater to the building where it is piped to the toilets, and to the outside taps.

How much treated mains water can a system save?

Depending on your normal usage, it can save 30 to 50% of the treated drinking water from the mains in houses and up to and up to 80% of the treated drinking water in a business or commercial building.

How much would this save on water bills?

Depending on your normal usage, it can save 30 to 50% for the domestic user and 80% for the commercial user of the treated drinking water from the mains. Having metered water is the best way of appreciating the difference.

How much rainwater does a system collect?

This depends on the area and angle of your roof, and your rainfall. Averages of 100,000 litres per household are commonly quoted, much more for large roofed commercial buildings.

What can you use the water for?

Filtered, untreated rainwater should only be used for non- drinking or bathing purposes: toilet flushing, gardens and vehicle or yard wash downs.

Is it only for new buildings?

No, it can be installed in existing buildings. Garden systems can easily be installed in existing buildings. Home systems are more appropriate when more extensive works are planned.

Is it only for houses?

No, bungalows and commercial premises are also very suitable, the only limitation is the area of the roof to capture rain, compared to the number of users; this puts a limitation on the use for flats and apartments, but it could supply a viable source for garden use.

Where is it installed?

The tank should be buried under a driveway, landscaped area, garden, or patio, with space left for the round access cover. There is a cast iron lid available which can accept cars driving over it , if suitably installed.

Are there any grants available?

Not for domestic installations yet, although several organisations are petitioning the government for assistance. For commercial installations, there is a tax relief scheme (ECA) for suitable approved equipment on the Water Technology List.

How clean is the water?

The rainwater is filtered as it enters the storage tank, to remove particles and other matter. It is kept in the dark and kept oxygenated to discourage algal growth, and properly designed systems are designed with calming inlets, which ensure that any sediment at the bottom of the tank is not stirred up. The water is not drinking water fit for humans.

Could rainwater get into my drinking supply?

Not in a properly designed system, the pipework is entirely separate and should be identified as non-potable ( Not for drinking)

Do I need a big roof area to make it worthwhile?

The bigger and flatter the roof area, the more rain will be captured, and the more the rainwater will substitute for treated mains water.

What happens when there is no rain?

When there is a prolonged spell without rain, the water level in the storage tank will fall to a minimum level. At this level, a float switch will open a valve from the normal mains supply and keep the storage tank on the pump unit topped up, until the main underground tank is filled by rain again. Garden only systems, as standard, do not have mains water backup in times with no rain.

Can it be used when there is a hosepipe ban?

It is possible to use a hosepipe connected to a rainwater tank, provided that the tank is not connected to a mains water supply. Many people are doing this already by using a water butt.

How is the system maintained?

The internal filter should be washed about once a quarter, otherwise maintenance is not needed. However, several filters are self-cleaning. The only moving components - pump and float switch have an extremely long life. The system should be designed to overflow a few times a year, to remove floating matter. The supplier offers a maintenance contract and this can be arranged by calling the helpline on 01608 665460. It is important to ensure that your gutters and down pipes remain clean and open to maximise the amount of water collected.

Is Rainwater harvesting a new idea?

No, collection and re-use of rainwater from roofs can be traced back thousands of years in hot, dry countries around the Mediterranean. In continental Europe, some 100,000 are installed annually; Germany has been using and refining the technology since the early 80s.

How will it affect my domestic appliances?

If you are in a hard water area and install a rainwater harvesting system, white goods, such as your washing machine, often last longer and run more efficiently. Harvested rainwater is soft and so the machine will not build up internal limescale and shorten its lifespan. An additional benefit in hard water areas is that less detergent is required which means fewer pollutants released into the environment and a reduced cost of cleaning materials.

Why should I buy one?

Because the system will generate significant environmental benefits through reducing mains water demand and reducing storm water run-off. In addition, with water bills expected to rise 10% a year for the next five years, then the payback period will be reduced further. Also, control of storm-water run-off is now increasingly a planning issue which rainwater harvesting systems can play an important part in addressing.

How long will it take to install?

Depending on who installs the system, typically the tank can be installed in one day thanks to no concrete being required and only a gravel surround, with the drainage connected to the filter etc. The pump packages will then vary in lengths of time to install. Garden packages should be possible to install within a couple of days.

Can the down pipes go into open gullies at the bottom?

The downpipes should be fully sealed from the connection at the gutter on the roof right through to the tank. Open gullies should not be used at the bottom of the downpipes as this will let surface water into the tank which could have oil, fuel or other contaminants in the water. Only rainwater that falls on to the roof should be used for rainwater harvesting.

Does the tank have to be surrounded in concrete?

No. The Graf Platin tank does not require and should not be surrounded in concrete. Only a gravel surround is necessary to backfill the tank, as per the tank installation instructions.

Where is the pump installed?

The Home system uses the Eco-Plus pump package which should be installed inside the home, either in utility room or garage for example. This pump package also provides the mains water top up in times without rainfall, when required. All moving parts are out of the tank and therefore accessible. The Garden only system uses a submersible pump inside the main underground tank. This pumps to a hose connection box in the garden.

Which is the right system, or tank size for your home?

Contact the Helpline on 01608 665460 to discuss your specific requirements and the team can advise of the best system and tank size for your home and also on installation.

In the unlikely event of a problem, or if you need to know more.

Contact the Helpline on 01608 665460 to discuss the specific problem you are experiencing with your system. Please have details of the problems you are experiencing to hand and be available to answer some exploratory questions on your system. Depending on your enquiry, you will receive a response to your enquiry within 24 hours to assist with getting your system running again as quickly as possible.

If there is too much rain and the tank is full, how will the system overflow?

The tanks will overflow to either a soakaway or to mains drainage. The filter package includes an overflow siphon (u-bend trap) which is fitted into the top of the tank and an underground pipe connects to this (from top of tank dome) to remove overflowing water to either a soakaway or mains drainage system.

Connections and the pipes needed to fitted to the tanks. Are these different to the ones already fitted or will any existing need to be changed?

The connections to the top of the tank will all be 100mm diameter underground pipe, as used as standard from the connection at the bottom of each downpipe. If the system is being retrofitted then existing pipe should be able to be moved/used to incorporate into the system. For new build projects the same pipe would be used as standard, with or without a rainwater harvesting system.

Any need to change guttering to make the system more efficient?

This should not be required. The only types of buildings where this may be applicable is on old agricultural or outbuildings which may have asbestos guttering. If this is the case then it would be advisable to change to this plastic guttering.

Do customers feeding the non-potable water in the home off of a rising main need to re-plumb the house?

When retrofitting a full domestic system it will be necessary to change some of the existing plumbing. It should not be necessary to re-plumb the whole house but the pipes to the toilets or washing machine ( or any appliance to receive harvested rainwater) will need to be connected to the pump unit. A mains water connection will be required at the pump unit, which is normally installed in a utility room or garage for example. We would suggest that full domestic systems being retrofitted are referred to the help line where we will try and assist with a site survey and the option of installation assistance.

What sort of pumps are needed in the home as well as in the system to get the water in to the house and then up to first or second floors?

The standard home system supplied will provide all necessary pumps. The only additional pump that may be required is on the home system if there is a greater distance than 15m between the underground tank and the house. Standard home and garden systems will only need the items sold in the complete packages.

What sort of pump is best for what sort of use?

The garden system is for garden use only. The home system includes the home pump package which is suitable for WC flushing, washing machine and external taps.

Are there issues with the water meters in regards to connections or who owns the rain issues with water boards?

The mains water will be supplied to the pump unit and will still be metered on supply. There is no charge for collected rainwater and this will not be metered, just collected and reused as required.

How do you keep animals outside of the system?

The filter packages for both the garden system and home system include rodent guards to prevent animals entering the tank.

Installation and maintenance

Installation of a Rainwater Harvesting System is easy. The underground systems are manufactured to the highest standard and are designed to be simple for DIY installation. They are comparatively lightweight and do not need to be concreted in place.

For more detailed instructions, here are installation and maintenance guides for our most popular Rainwater Harvesting Systems:

• House & Garden Rainwater Harvesting System [ 150 KB ]
• "Garden Comfort" Rainwater Harvesting System [ 176 KB ]
• Underground Rainwater Tank [ 1.3 MB ]