The benefits of rainwater harvesting systems

Every cloud has a silver lining and if there was ever a positive to come out of Covid it is a greater appreciation of what clouds bring us – rainwater.

Research during the pandemic showed a more genuine regret for our impact on the environment, some of which was evidenced by the clearer skies and lower pollution levels caused by the massive drop in air travel and industrial activities.

This greater respect for the environment saw sales of rainwater harvesting systems hit new heights. Some manufacturers reported 100% increases in sales of above-ground systems such as water butts (which capture about 500 litres of water) and 50% increases in below-ground pumped systems (for the garden only as well as for the garden and house) which can filter and store up to 10,000 litres.

Far-sighted manufacturers believe that designing rainwater harvesting systems into all new-builds, regardless of whether they are domestic or commercial, should be mandatory, even in the UK – a country with relatively high rainfall.

This would also help to relieve the burden on water utility companies which are already struggling with demand and the cost and inconvenience of repairing leaking water pipes which do not differentiate between drinking/potable water and grey/non potable water.

In the UK, up to 50% of the 150 litres’ daily usage for the average person (excluding garden irrigation) could be saved if they used harvested rainwater to flush their toilets and clean their clothes.

At a time when the price of drinking water has increased by 500% over the past couple of decades, this could save up to 50% on a water bill. If people also used recycled rainwater to water the garden and plants, they could save 60l/m² per year of potable water.

As well as being environmentally sound, rainwater harvesting conserves ground water resources, reduces demand on potable water supply and mains water consumption in areas where water is scarce, as well as the energy consumption needed for the purification of drinking water, and contributes towards flood prevention and stormwater management.

And the days of eyesore water butts are long gone. There are now contemporary, discreet designs made from recycled materials that even the fussiest property owner would be proud to have in their garden.

But this interest in rainwater harvesting means there is now a perplexing plethora of options on the UK market. They come in many different shapes and sizes, with some suitable for over-ground storage and some for the more discreet underground.

Perhaps the most important consideration when choosing which [underground] one is right for you is the ground water level on the site you are going to be installing the system on.

If the water table is high, low-profile shallow tanks can be completely submerged in ground water and still be guaranteed to stay in the ground, even though the pressure of the ground water surrounding them could cause them to pop up out of the ground.

Tanks installed in ground water should have vertical hole features so the ground water can surround them and pass up through them without building up pressure from underneath and around the sides, which pushes against the tank and causes it to pop upwards.

Another important consideration is whether the rainwater harvesting tank you choose requires a concrete or a granular gravel backfill. Sometimes this depends on the type of tank, or the depth in which it is being installed, and it can also depend on the loading which is going to be imposed on top.

Tanks that require a concrete surround typically take longer to install and so the labour costs can be more expensive. Concrete is also more expensive than gravel. Tanks that require a gravel surround can generally be installed in as little as half a day. Because the gravel can simply be backfilled and compacted in layers, you don’t have to wait for it to set like concrete so it’s much quicker.

Whichever installation method is used, it’s vital the manufacturer’s instructions are followed so their warranties will stand. Many tanks are provided with warranties of 10+ years but your contractors should follow the instructions to the letter to ensure responsibility lies with the manufacturers even once the tank is in the ground.

Another important consideration is whether the filter is an internal, integral part of the structure or it’s an external pre-tank filter which requires two access covers and two manhole lids. If the filter is inside the tank, one lock on the top gives easy access to the filter.

Cleanliness inside the tank is of paramount importance because its water is going to be used for your washing machine, flushing toilets and your outside tap. If dirt or soil, or bits of gravel or stone, find their way into the tank during installation because the access points have not been covered, it could mean the tank has to be completely cleaned out as soon as it starts to be used.

Ensure the tank is installed with the access covered or the lid temporarily already on, and that the people installing it are aware it’s not a septic tank! Yes, it has happened!

Finally, consider what type of lid you require. On most tanks you’ll have two options – a standard lid with pedestrian loading for a garden or a driveway-loading lid. These are usually cast iron and will take a light traffic load, typically a car or van. But if the tank is being installed in an access road where lorries and HGVs may pass over it, then this must be considered to ensure the lid, and the tank underground, is capable of withstanding the load above it.

Many people likened the Covid crisis to a war. With just 0.4% of the planet’s fresh water being available for 7 billion people, rainwater harvesting champions are unhappily convinced the next war will be about water.

So best, like them, start harvesting it now.