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A quick guide to rainwater harvesting

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Graham Mann
I have been in the Water & Waste Water industry for 30 years and formed a Water Consultancy business called H2o Building Services both myself and my team have built a wealth of knowledge and expertise Saving companies money on their Water bi


  • quick guide to rainwater harvesting

This summer may well have been something of a wakeup call for businesses and individuals alike, with the intense temperatures recorded in July and August revealing just how vulnerable the system is, especially where water is concerned.

In fact, the Environment Agency has just agreed that the entire south-west of England is now in drought after some of the driest conditions seen in almost 90 years.

This has been triggered by hydrological position, such as river flows, rainfall, ground and reservoir levels and soil dryness, as well as the impact on the environment and abstractions.

The result is that, while essential water supplies are still safe, both Defra and the Environment Agency are now calling on water companies to continue with precautions to protect these resources should we see a dry autumn.

Environment Agency drought lead Chris Paul said: “Despite some heavy rain over the past two weeks, it has not been enough to refill our rivers and aquifers.

“River levels across our Wessex area are exceptionally low – many showing the lowest flows on record. This places incredible strain on local wildlife and this is why we are moving to drought status. We are prioritising our local operations to minimise impacts on the environment.”

Businesses, too, have their part to play in safeguarding water resources and reducing their reliance on mains water, which will help protect the environment and build resilience within organisations so they can continue operating, no matter what happens externally.

Rainwater harvesting is a particularly effective alternative to mains water supplies, with the water that falls across your site collected and stored for future use.

How does rainwater harvesting work?

Once rainwater is collected from rooftops and other impermeable surfaces, it can be passed through a filter to remove any contaminants. It then goes into a holding tank, which can be positioned strategically somewhere on the premises, fed by the gutters installed around the property (if for domestic use).

Such systems typically feature components including the tank and collection pipe, treatment, pump, cistern, distribution pipe and controls.

Tank materials can include concrete, brick or steel and it’s essential that they’re designed to ensure that inflow of contaminated groundwater cannot happen.

If the tanks are going underground, they’ll also need to be able to resist vehicular and surcharge loads, as well as backfill pressures. If tanks are going to remain above ground, it’s important to protect them from freezing, as this could cause cracking and lead to leaks. Using the appropriate insulation can help prevent this, however.

A mains backup is included in these installations, with float switches fitted inside the storage tank that can sense when water levels have fallen too low. At this point, the feed opens to refill the tank with mains water instead.

The different types of rainwater harvesting system

There are various different types of rainwater harvesting system and the right one for you will depend on what you intend to use it for. You may also find that you could potentially benefit from using one or more different types to address different issues across your site.

Options include water butts, direct pumped systems (submersible/suction), indirect gravity/pumped, gravity only, retention ponds and in-ground storage.

Water butts are perhaps the most simple system of them all and generally have smaller tank volumes, which is why they’re ideal for domestic use. They can also be used effectively for farms, stables and so on, with the stored water used for applications such as gardening and washing the car.

For smaller businesses, a submersible pump of some kind may be a good option to consider. These systems are easy to install and can help pump water directly to toilets, washing machines and other such appliances.

Where you’re based may also have an impact on which system is the most appropriate for you and your site. You may find, for example, that underground tanks are the best option if you operate somewhere that sees heavy rainfall in one season.

And the industry you work in could also help inform your decisions when it comes to selecting a rainwater harvesting system.

For example, those in the agriculture sector could consider investing in retention ponds, which collect surface water runoff and improve the quality of this water through sedimentation, soil filtration and decomposition. This water can then be collected to be used elsewhere, such as irrigation and livestock watering.

How can businesses benefit?

Business use of these systems is on the rise around the world and it is an effective way to reduce mains water usage – sometimes quite significantly.

From a financial perspective, after the initial investment is made, a rainwater harvesting system represents a solid opportunity to reduce operating costs, which will have a big impact on your water bills.

Modern systems are so effective that they operate alongside mains water supplies, which means that when harvested supplies do run out, the switchover to mains is seamless – so you won’t experience any disruption to your business operations.

From an environmental perspective, rainwater harvesting can reduce the amount of surface water runoff during periods of heavy rainfall, easing pressure on the pipe network and helping to prevent flooding.

With hosepipe bans having recently been introduced around the country following the dry conditions during the summer, there’s no time quite like the present than to consider how best to go about reducing water consumption.

Droughts are expected to become more frequent and more intense as times goes on, in line with climate change and rising global temperatures, so it may well be that harvesting rainwater becomes a more pressing necessity as time goes on to help ensure that it continues to be business as normal, even in the face of water shortages.

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