We can answer this question in just a few words: Don’t worry, underground water collection systems are entirely safe. However, it is fair for customers and property developers to ask questions about the safety of the containers and the water stored in them, especially when the water is destined for human use.
In this article we hope to set your mind at rest by considering two important concerns regarding underground rainwater tanks: the security of the tank itself, and the quality of the water stored within it.
Most domestic rainwater tanks are capable of storing at least 1,500 litres (330 gallons) of water, and frequently will hold 3,000L or more. Tanks on commercial properties can store vastly greater volumes.
Even a small volume of water can present a risk, especially to young children or pets. This has the potential to be a serious hazard as it is often very difficult to escape from the main body of the tank; the access shaft offers a restricted opening and can sometimes be deep. It is very important therefore that any tank has a cover which is securely fitted and is either fixed in position with screws or bolts, or is a heavy duty cover (i.e. one that is too heavy for a child to lift and requires special tools to remove).
Underground tanks are defined as ‘confined spaces’ and should only ever be entered by trained personnel equipped with the correct safety gear. Fortunately, it is rarely necessary to enter a rainwater tank, providing there is adequate filtration and it has been correctly sized to prevent stagnation.
A well designed system will incorporate features to ensure the quality of the water and limit the need to access the tank interior;
- Good pre-tank or in-tank filtration of 0.5mm or less
- Oxygenating calmed flow of the incoming water
- An overflow trap to exclude foul odours from the drains
- A backflow protection device (non-return valve) on the tank overflow
- A pump that is reliable and equipped with a fine suction filter
- A pump that can easily be extracted from ground level
- A secure child-proof access cover
Attention to such detail will ensure that it is only necessary to open the tank once per year to check the pump and clean the suction filter.
Larger tanks used on commercial properties will sometimes have access ladders to enable easy access for maintenance, particularly where the main filter unit is fitted within the tank. Even so, entry must only be attempted with correct safety equipment and one or more people present above the tank entrance to assist escape.
Modern underground storage tanks are generally manufactured from polyethylene or GRP (fibreglass), and less frequently, from pre-cast concrete. Most polyethylene tanks are rotary moulded as a single piece, avoiding the need for welded joints and eliminating the risk of leakage. GRP tanks will be moulded in sections and then joined together at the factory. Inlet and outlet connections must be fitted with seals both to protect against leakage and also to prevent ingress of soil or dirty water from the surrounding ground.
The important element of any harvesting system is the primary filter that prevents leaves, twigs, moss etc. from entering the tank. At Rainharvesting Systems, we supply market leading precision-made filters manufactured by Wisy AG of Germany. The company manufacture a range of rainwater filters using high grade 1.4301 stainless steel; larger models are supplied fitted within a vehicle-duty polypropylene housing.
Rainwater harvesting systems are an increasingly popular choice among homeowners, with many property developers responding to this need by installing them in new build properties. A well designed rainwater harvesting system is safe, efficient and will save the end-user a good deal of money over its working lifetime. They are also cheap and easy to install during the house construction phase, avoiding any potential disruption to end-users.
Our FREE Guide To Rainwater Harvesting Systems
To find out more about the benefits of rainwater harvesting, including the value they can add to a property development, click here to download our free Rainwater Harvesting Guide. If you would like to discuss your project with one of our sales advisors, please give us a call directly on 01452 772000, or send an email to