An Overview of Rainwater Harvesting Systems

Rainwater harvesting (RWH) systems are not new. For centuries people have collected and stored rainwater close to where it falls and used it for a number of purposes, such as drinking, irrigation, watering livestock and general household use. In most developed countries the wide-spread introduction of centralised water supply systems has meant that RWH systems have largely fallen out of vogue. However, in recent years there has been a renewed enthusiasm for them in many developed countries. Reasons for this renewed interest include:

• The escalating environmental and economic costs of providing water via centralised water supply systems
• Potential cost savings associated with using rainwater in place of metered mains water
• Benefits of rainwater over mains water for certain end uses e.g. rainwater is better than mains water for garden irrigation purposes because of its chemical composition
• The implied sustainability benefits of using rainwater in place of mains water gives them an added attraction for environmentally-conscious citizens

However, there are still a number of issues surrounding the use of RWH systems that have acted as a barrier to their wider implementation, particularly in the UK. The mains areas of concern are:

• Uncertainty about future costs. Whilst capital (installation) costs can be predicted with a fair degree of accuracy, longer term costs (such as the potential reduction in water bills, maintenance costs of RWH system etc) are harder to forecast
• Climate variability. The weather is notoriously hard to predict with any degree of accuracy (although if you live in the UK then there is a fairly good change that it will rain on any given day!) and so likely rainfall patterns, and therefore than amount of water available from the RWH system at any given time, are hard to determine
• Uncertainty over water demand patterns. Water usage within any given building is likely to vary from day to day and predictions of water demand may have a large margin of error

These three issues can (and often do) combine to act as a deterrent to installing a RWH system.

To help overcome these issues, we developed an application called RainCycle which is a spreadsheet-based hydraulic modelling and whole-life costing tool aimed at addressing the above issues.

Click here for further information about RainCycle

Also see the Useful Links section for other websites about rainwater harvesting.