What is Rainwater Harvesting?

What is rainwater harvesting?

What is Rainwater Harvesting?

Rainwater harvesting is the collection and storage of rain water, rather than allowing it to run off to ground. Rainwater is collected from a roof-like surface and redirected to a tank, either above ground or underground, to be used within the home and/or garden. 

As the population grows, demands on mains water continues to rise. Coupled with consumer demand for companies to reduce their environmental impact, rainwater harvesting is increasingly sought after by both the public and commercial organisations.

Why Harvest Rainwater?

The average household uses around 150 litres of water per day, just 3% of which is for human consumption. Rainwater harvesting is a sustainable solution to rainwater management challenges.

  • With a properly implemented rainwater harvesting system in place, it is possible to use up to 50% less treated water without any effect upon levels of hygiene or comfort.
  • Provide your garden with water during dry spells, i.e. hosepipe bans.
  • Aid in preventing localised flooding, as the collected rainwater acts as part of the Sustainable Urban Drainage System (SUDS).
  • Provide home users with soft, lime scale free water for washing machines, dishwashers, toilets. Decreasing the need for descalers or breakdown fees due to build up.


What can Rainwater be used for?

Rainwater can be used for watering gardens, washing cars, livestock, irrigation, domestic use such as cleaning, washing machines and toilet flushing, and domestic heating. The harvested water can also be used as storage for fire-water and in commercial and manufacturing processes.

Rainwater is not suitable for drinking or for use in showers and baths. Rainwater is generally free of harmful minerals and in most cases chemicals but can be adversely effected by air pollutants and/or contamination by animals in the catchment area. The only way rainwater can be used for drinking water is if it is treated by ultraviolet filters, which are not practical for domestic use as generally a rainwater tank will not store enough water for total consumption in a domestic situation.

rainwater tank

Why install a Rainwater Harvesting System?

In many new builds, the council require that a rainwater harvesting system be installed to take pressure from the existing already under pressure water system. In retrofit buildings, using a rainwater harvesting system reduces the stormwater run-off. It makes washing machines run more efficiently by using less detergent as the water is softer and prevents the build-up of limescale in appliances. Rainwater is also kinder to plants for garden watering.

To see our full range of both above ground and underground rainwater harvesting systems click Rainwater Harvesting Systems

Are there any Rainwater Regulations?

Rainwater (or any other non-potable water) must be kept totally separate from mains water. 

Harvested rainwater should run through a totally independent set of pipes, use different and unconnected storage tanks, and all pipes and fitting must be clearly marked as being Not Drinking Water. Another useful source of information is the Water Regulations Advisory Scheme (WRAS).

How do I size my Rainwater Harvesting System?

The size of a rainwater holding tank must match the demand for water with its availability as closely as possible. BS 8515:2009 provides an authoritative and industry-approved means of calculating the optimum size of tank for household water use. Unlike other industries it is better to reduce the size of the tank rather than oversize it if in doubt as to the requirement. This is due to the benefit of allowing the tank to overflow at least twice a year to flush out floating debris. The tank chosen must therefore be a balance between rainwater supply and water demand. In order to correctly size the tank, the capacity should be the lesser of either the rainwater supply or the water demand. A worked example demonstrating this principle is shown below:-

Rainwater Demonstration

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