Rainwater harvesting independent advice

Rainwater has been harvested – or collected, stored and then used when needed for hundreds, if not thousands of years. Rainwater harvesting remains a standard technique in many parts of the world without mains water, or accessible groundwater.

Most areas of the UK have mains clean water supplies. Increasing demand is however been put on this limited mains system and there is greater consideration of the value of making developments more sustainable.

All mains water is treated to a high drinking water standard, yet the vast majority of mains water is used for purposes that do not require such standards. The most obvious areas of use are where the quality of water is less critical, such as car washing, garden watering and toilet flushing.

Rainwater harvesting can be considered as a source control system – it that it can contribute to reducing the overall discharge of water off a site and can provide some limited attenuation.

There are several downsides and every proposal should be considered on a case by case basis by an independent professional civil engineer with experience in the assessment and integration of such systems within an overall site water and drainage scheme. There are many manufacturer harvesting products which can be purchased “off the shelf” and with “free sales advice”. Their role as manufacturers is to provide a system which is “fit for purpose” not provide you with independent professional advice on the various systems, operations and integration of the system with the rest of your drainage.

The Environment Agency advices:

  • Each proposal should be examined [by a experienced professional engineer] on a case by case basis.
  • The effectiveness of rainwater harvesting schemes varies considerably and depends on the sector and scale.
  • Simple water efficiency measures should always be considered before rainwater harvesting.

How to maximise value of a rainwater harvesting system

The integration of a harvesting system is therefore critical to how beneficial it will be. Essentially a system is more efficient, where the clean catchment and the usage of such collected water are maximised, with minimal construction spend. However, it is often more complex, the optimal location often relates to the configuration of the existing or proposed surface water drainage.

In effect this often means:

  • only collecting from part of a site where the rainwater harvesting system can be installed cost effectively.
  • only serving the locations of a development with maximum use.

For example, this could include collecting across a number of standard roofs and then feeding a toilet block with a outside tap. This avoids the costly duplication of water pipework throughout a complex. As public facilities usually have larger roofs and greater usage they tend to deliver more cost effective systems.

With careful consideration of quantity and quality of flow it is possible to combine the systems with the backwash flows from swimming pools, essentially turning a discharge, back into a valuable asset. In deed it is often the complex integration of such systems which maximise the value for private and public sector clients.

At Wilsham we are one of the most experienced independent consultants in the UK in the integration of rainwater harvesting systems with existing and proposed drainage systems.