A third of all domestic water is used for non-potable purposes – from flushing toilets and watering gardens to washing clothes and cars. Barrie Smith – Area Sales Manager at Graf UK – discusses rainwater harvesting, including the different systems on offer and what installers need to know to get the best out of them.

Rainwater harvesting (RWH) makes perfect environmental and economic sense – providing a simple but effective way to collect and reuse rainwater for a range of applications. Therefore, it’s no surprise that demand for RWH is steadily on the rise, especially in parts of the country with low rainfall and a higher risk of water shortages, such as London and the South East.

This is all good news for plumbers, who already have the skills needed to fit RWH solutions. But to maximise the business opportunity at hand, they need to be fully aware of the scope of systems on offer as well as the wider factors to consider when specifying, designing and installing.

Let’s look at the three main RWH options on the market.

Direct systems

Direct systems are the most common RWH option for both domestic and commercial applications and operate by gathering water in an underground storage tank and pumping it directly to the points of use such as toilets and washing machines. They usually feature a controller that detects when water is needed e.g. when taps are turned on, or when the valves on washing machines and toilets are opened. This triggers the pump to supply water directly to the appliance.

Indirect systems

Indirect systems work by collecting water in an underground storage tank, pumping it to a header tank (typically situated in a property’s roof space or roof plant room), and then gravity-feeding it to the points of use. Suitable for both domestic and commercial applications, in the case of a power failure, indirect systems will automatically switch to mains water when water levels fall below a certain point in the tank.

Above-ground systems

Gravity-fed, above-ground tanks are the most energy-efficient RWH option. They can range from water butts (ideal for small-scale garden watering) to larger tanks, where water is required for a wider range of domestic or commercial uses.

However, the latter are not suitable for all buildings because they require significant roof space. Even where this space is available, substantial structural support is often needed to bear the weight of the water safely, which can incur extra costs. For these reasons, it is recommended to use underground tanks where possible.

Installer checklist

Once familiar with the different types of RWH systems on offer, there are several factors to bear in mind during the specification, design and installation stages to ensure best results. The following are some key considerations.

• Property type and usage

This may sound obvious, but the first thing that needs to be established is what kind of building the RWH system is for, how many occupants it has, and what they will use the water for.

Will the water just be needed for the garden, or will it be used for toilets and washing machines inside the home? If it’s the former, the installation job will be much easier because it won’t be necessary to connect the tank to any internal plumbing and pipework. Garden-only systems, such as Graf UK’s Platin Garden Comfort package, can generally be retrofitted at any property with enough garden space to accommodate the tank. For domestic-supply systems, siting is slightly more complicated.

• Sizing and siting

It’s important to choose a RWH tank with the correct capacity for the required usage – and this will depend on the property’s size and number of residents. When it comes to siting the tank, if the rainwater is for indoor use, it’s crucial to consider the location of the utilities that it will be supplying. The closer the tank is to the points of use, the less pipework will be needed and the more straightforward the job will be.

Garden-only systems can be sited virtually anywhere because they hook up directly to the hose or sprinkler. Pop-up lawn watering outlets can be connected to the RWH tank underground and can therefore be sited several feet away – allowing for hassle-free watering of the whole garden without having to stretch the hosepipe.

• Tank design

Depending on the kind of tank chosen, it may need to be sited on a concrete base to aid stability and prevent movement. Constructing this base can be both costly and time-consuming – in fact, it can often be the difference between the install taking one day or two days – so it’s worth looking around for a tank that doesn’t require this. The amount of digging required to accommodate an underground RWH tank is also something to bear in mind – again, this can add time to the job.

• Soil type and soakaway

Every RWH solution needs a soakaway to manage overflow. There are two types of soakaway – attenuation (where water is retained and then slowly discharged into the surface water drainage system or water courses) and infiltration (where water is gradually released back into natural groundwater reserves). Before deciding which type of soakaway to install alongside a RWH tank, it is necessary to find out the soil type.

Many parts of the UK have clay-heavy soil, which isn’t suitable for infiltration – and as such, attenuation soakaways are more common in this country.

Opportunity for business

The rainwater harvesting opportunity for plumbers is plain to see. Those who arm themselves with the right knowledge and expertise now will be in pole position to benefit well into the future. With the continuing installation of water meters throughout the UK, more homeowners (and business owners) will be looking for ways to reduce costs