Rainwater Harvesting Storage Tank Installation Graf
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Rainwater Harvesters Explained

Every time it rains, the building guttering system sends the water into soakaways and the sewage system.

Install a rainwater harvester, and this valuable resource can be collected and stored ready for a multitude of uses where water does not need to be of drinking quality, such as flushing the loo, washing clothes in a washing machine, watering the garden, washing the car and topping up garden ponds.

What Is A Rainwater Harvester?

Rainwater harvesters are large tanks buried in the ground which are connected to guttering downpipes. A filter removes larger particulates and a pump sends the water to feed taps and/or hose pipes. Domestic properties which have a rainwater harvester can reduce their mains consumption by up to 50%, although savings of 20-30% are more usual. They can also be used in commercial settings such as shopping centres, schools and sports stadiums. These buildings have large roof spaces and higher demand than domestic properties, so rainwater harvesting can be a logical as well as environmentally-friendly approach to the water supply.

What's The Purpose Of A Rainwater Harvester?

Rainwater harvesters reduce the overall volume of water that needs to be processed at water treatment works to get it up to drinking water standard. This takes pressure off the system, especially in times of drought or where demand outstrips supply. In the UK, population growth, changes in lifestyles and changing climate are all putting pressure on our ability to keep up with demand. The Environment Agency states that: “In the South East of England, where large numbers of people live and work, water is scarcer than anywhere else in England and Wales. In fact, there is less water available per person in this region than in many Mediterranean countries.”

Graf Rainwater Harvester House Cutaway

Rainwater Harvesters From Drainfast

Drainfast supplies rainwater harvesters manufactured by the German company GRAF. GRAF places great importance on the quality and durability of its products and offers a warranty of up to 15 years on its rainwater harvesters. Germany is the world leader in the manufacture and installation of modern rainwater harvesting systems and GRAF has long been an innovator in this area.

There are four main components that make up a rainwater harvesting system: The tank, tank cover, pump and filter. There are various options available to allow complete customisation to produce the perfect solution for your site.

Tank Options

Graf Carat S Rainwater Tank


Carat S

This ingeniously designed tank is manufactured to the highest possible standards using injection compression moulding. The tank is strong, durable and easy for the end user to operate. The rotating tank dome helps the installer to easily align the head with the connections. All installation pipes are connected using the five standard lip seals. A telescopic dome shaft connects the system to the ground surface and is designed to allow the lid to be completely flush with the finished ground level.

Carat S tanks come in a range of sizes: 2700, 3750, 4800, 6500, 8500, 10000 & 13000 litres.

Carat S tanks come with a range of modular components to choose from – filters, hose connection boxes and pumps – for either purely garden use or for both home and garden use. Speak to our technical team to discuss which options are right for your site and budget.

Overview of Carat Rainwater Harvesting System

GRAF have produced a short video which shows how the Carat tank can be used and installed:

Watch Operating and installing a rainwater harvesting system on YouTube.
Graf Platin Rainwater Harvesting Tank Large


The Platin flat rainwater tank has a smaller minimum installation depth than the Carat round tank so is a good choice where ground depth is limited. It can be cheaper to install because less digging is required. They are easy to assemble using GRAF’s range of modular components; the telescopic dome shaft allows for easy adjustment to get the cover flush with the ground surface. Once installed, the only part that is visible is the tank cover.

Platin tanks come in a range of sizes: 1500, 3000, 5000, 7500, 10000 & 15000 litres.

Platin tanks come with a range of modular components to choose from – pumps, connection boxes, rodent guards and covers – for either purely garden use or both home and garden. Speak to our technical team to discuss which options are right for your site and budget.

How to Install a Platin 1500L Tank

GRAF have produced an excellent video which shows the simple steps needed to install a Platin Tank

Watch Graf Platin Rainwater Harvesting System on YouTube.

Tank Domes, Shafts & Covers

There are various dome shaft and cover options. The shaft gives easy access to the filter and tank post-installation for occasional maintenance.

For pedestrian loading

Choose from Mini (140mm-340mm earth covering) or Maxi (140mm-440mm earth covering) telescopic dome shaft – both with green PP cover and childproof lock.

For vehicle loading

Lightweight vehicles - choose the telescopic dome shaft with childproof cast iron cover – suitable to bear loads of up to 3.5 tonnes. 140mm-440mm earth covering.

Heavier vehicles - choose the lorry-bearing telescopic dome shaft. For the lorry-bearing shaft, concrete rings and cover will need to be purchased. 140mm-440mm earth covering.


There are a variety of pump packages available with all the accessories you need for installation. You’ll need to consider whether your chosen rainwater harvester is for garden use only or is also to be used for indoor supply. Please call our technical team for information and advice.


Both the Carat S and Platin have 3 different filter packages to choose from. Water systems which are for garden use only will require less filtration than those to be used for domestic applications such as loo flushing or washing machine. Please call our technical team for information and advice.

How to Order Rainwater Harvesters from Drainfast

1) Speak to our technical team by calling 01730 774000 to discuss your site requirements. They will advise which components are best to use and will provide you with a quotation and delivery lead time.
2) Place your order.
3) Delivery will be in 1 to 3 weeks depending on which items you require.

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