Get your water supply from the sky!


Matthew Rolph, MD, Graf UK

In the UK, one third of all domestic water is used for non-potable purposes such as flushing toilets, watering gardens and use in washing machines – and consequently does not need to be of drinking quality. With this in mind, rainwater harvesting (RWH) makes both financial and environmental sense, as it provides an easy and efficient way to collect rainwater for reuse in and around the home.

So it’s really no wonder that uptake is on the rise, especially in densely populated urban areas with a higher risk of water shortages (such as London and the South East). In these regions, water companies are actively encouraging consumer investment in rainwater harvesting as a way of reducing pressure on the potable mains supply.

The good news is qualified plumbers are naturally placed to reap the commercial benefits of this growth market, as they already have the skills needed to fit RWH systems. But it’s crucial that those adding this to their offering familiarise themselves with the market first – as this is the best way to ensure they specify the right system every time. So what are the main domestic RWH solutions available today, and what do installers need to know about them?

There are three main types of rainwater harvesting systems installers need to get to grips with – each with its own set of features, benefits and capabilities. The guide below gives a quick overview of these options and highlights the applications in which they will deliver best results.

Direct systems
This type of system works by collecting water in an underground storage tank and pumping it directly to the point of use. They are the most common RWH option for both domestic and commercial applications, and typically feature a controller, which detects when water is needed (for example when taps are turned on, or when the valves on washing machines and toilets are opened). In turn, this triggers the pump to supply water directly to the appliance. In some systems, this pump is submerged in the tank, whereas in others (e.g. our ECO-Plus system) it is built into the controls unit, usually located inside the house, garage or plant room – keeping the technology dry and shielded from the elements.

Indirect systems
The indirect variety is popular in domestic applications, but can also be suitable for commercial premises. They collect water in an underground storage tank and pump it to a header tank (usually situated in a property’s roof space or roof plant room). Gravity then feeds that water to the points of use – meaning indirect systems have much simpler (if any) controls than direct systems. Typically, a submersible pump will detect when the valve in the header tank opens, and simply pump water until it closes again. In an indirect system, valves are usually set to open only after three or four flushes of a toilet, for example. The pump is therefore in use much less frequently than in a direct system. In the event of a power failure, the system will automatically switch to mains water as soon as water levels in the tank fall below a certain threshold.

Above ground
Above-ground, gravity-fed tanks are the most energy-efficient RWH option. They can range from simple water butts (ideal for small-scale garden watering) to larger, in-roof tanks where water is required for a wider range of uses. As significant roof space is a prerequisite for the latter, in-roof tanks are not suitable for all applications and all types of buildings. What’s more, even where this space is available, substantial structural support is often required to bear the weight of the water safely – which can incur extra costs. This is why we at Graf UK recommend using underground tanks wherever possible.

Next steps
What are the next steps? Once you’ve gained a good understanding of the different RWH options on offer, bear in mind there are several other important aspects to consider during the specification, design and installation stages to ensure optimum results.

For instance, it’s crucial to determine the property type and establish what the water is going to be used for. Will it just be needed for the garden, or will it be used for toilets and washing machines inside the home too? This will help you calculate the required demand – and give you an idea as to how complex the job is likely to be.

The sizing and siting of the tank is also a key part of the equation. Determining the correct capacity of a RWH tank will depend on the property’s size and the number of residents. At Graf UK, our rainwater harvesting experts are always happy to assist installers at the sizing stage if there are any hesitations. When it comes to siting, remember: the closer the tank is to the points of use, the less pipework will be needed – and the more straightforward the job will be.

Depending on what kind of tank you opt for, you may also need to factor in a concrete base to aid stability and prevent movement in the groundwater. Building this base can be both costly and time-consuming, so it’s worth looking around for a tank that doesn’t require this. The innovative design of Graf UK’s Platin tanks means they are groundwater-safe, and therefore only need to sit on a gravel bed.

Last but not least, every RWH solution needs a soakaway to manage overflow. This can be an attenuation (where water is retained and then slowly discharged into the surface water drainage system or water courses) or an infiltration system (where water is gradually released back into natural groundwater reserves). At Graf UK, we would always recommend asking your manufacturer if in any doubt as to the best solution for a particular soil type. Our team of experts are also on hand to offer support when it comes to calculating the size of a soakaway. 

With demand for rainwater harvesting showing no signs of slowing, the opportunity for plumbing professionals is obvious. Those who garner the right knowledge and expertise now – and apply this at the vital specification stage – are setting themselves up to benefit well into the future.

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