A guide to Retrofit Rainwater Harvesting

Newly constructed buildings are often packed with the latest and greatest in green technologies but retrofitting these technologies into existing building stock is often dismissed as too costly and complex to retrofit. This common misconception is especially true for rainwater harvesting which has traditionally been viewed as too complex to install into an existing building.

Rainwater Harvesting for existing buildings is often dismissed due to concerns surrounding a lack of plant room space, the need for costly excavations for rainwater storage tanks, or simply, a lack of knowledge that rainwater harvesting exists on a commercial scale. Whilst these concerns may have been valid 20 years ago, rainwater harvesting technologies have developed considerably during this time.

This article will showcase why these exists problems surrounding retrofitting a rainwater harvesting system have been eliminated through new technology.

How much water is used in the UK?

Many are unaware that the UK is facing the prospect of water scarcity. The prospect of water shortages is caused by increasingly unpredictable weather patterns causing prolonged periods of droughts, increased flood risks and soaring populations which have all placed huge pressure on existing water infrastructure.

Recent announcements by the Environment Agency have suggested the UK uses around 14 billion litres of water per day and will need an extra 4 billion per day by 2050. The problem of water scarcity is already being felt by some regions in the UK which are now being classed as ‘seriously water stressed’ by the Environment Agency.

Most of the water which is used in both commercial and residential settings is made up of non-potable use rather than for drinking. ‘Non-potable’ water use is considered any water which is not fit for human consumption. In many buildings, potable water supplies are currently being used to flush toilets, supply irrigation systems and other vehicle wash activities. This is a huge waste of drinking water.

How can retrofitting rainwater harvesting increase water efficiency?

The need for widespread usage of rainwater harvesting cannot be underestimated. In fact, Rainwater Harvesting is a key part of the UK's plan for plentiful water.

In buildings without a rainwater harvesting system, rainwater is channelled straight into the existing sewage network and is transported many miles for treatment by a water company.

Rainwater Harvesting provides sustainable water supply by preventing perfectly clean rainwater from going straight into the traditional drainage network. Instead, rainwater from the roof area is channelled into a rainwater storage tank to be reused for a number of non-potable uses, including toilet flushing, laundry, vehicle washing, irrigation and some manufacturing purposes.

The sustainable water supply provided by a rainwater harvesting system also produces much less carbon emissions than traditional mains water supplies. Mains water supplies requiring complex transportation and treatment which a sustainable supply from rainwater harvesting does not require.

Considerations when retrofitting a rainwater harvesting system

• Roof area – a free-of-charge desktop survey will be conducted by our team to measure the collection potential from the roof area.
• Roof drainage – the location of roof drainage points will be assessed to check the feasibility of a rainwater harvesting system. If the building has a siphonic drainage system, the siphon will need to be broken prior to the rainwater entering the rainwater harvesting system.
• Occupancy – an approximate building occupancy will be taken to estimate water demand.
• Location of points of use – a site visit will be required to work out any installation requirements of the site and to assess the best location for the rainwater harvesting system.

What are the maintenance requirements of rainwater harvesting?

Like any electrical system, maintenance of the rainwater harvesting system should be factored in to ensure the greatest water efficiency can be achieved. It is recommend rainwater harvesting systems should recieve a bi-annual service and a tank clean every 2 years. Read more about rainwater harvesting maintenance requirements here.

Other ways to improve water efficiency

As well as rainwater harvesting, other water saving technologies should also be used to achieve greater water efficiency within existing buildings. Our friends at WaterWise offer a full list of water saving tips for businesses and homes.

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