Rainwater harvesting

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What is rainwater harvesting?

Rainwater harvesting is a technique used for collecting, storing, and using rainwater for landscape irrigation and other uses. The rainwater is collected from various hard surfaces such as roof tops and/or other types of manmade above ground hard surfaces. The most common way of collecting and using rainwater via roofs and guttering is in water butts  or containers and then use on the garden.

More sophisticated rainwater harvesting systems are not common in Dublin for the following reasons:

  • The relatively high cost of the systems especially if retro-fitting.
  • Concerns that the quality of the water may pose a health risk.
  • Requires some technical skills to install and provide regular maintenance.

It is important to evaluate the potential savings before investing in a rainwater harvesting system.


There are many advantages to a rainwater harvesting system

  • Makes use of a natural resource and reduces flooding and storm water runoff
  • Reduces the demand on the Dublin Region Water Supply System
  • Excellent source of water for landscape irrigation
  • Home systems such as water butt can be relatively simple to install and operate
  • If you have a metered account you can significantly reduce your annual water bill
  • Promotes water conservation

For existing premises it is generally more economic to reduce water use by fitting more water efficient appliances and changing habits and behaviours before considering the use of complex rainwater harvesting systems.  It is important to evaluate the potential savings before investing in a rainwater harvesting system.

General Information

Rainwater systems come in all shapes and sizes, from simple catchment system like the water butt to large above and/or underground cisterns with complex filtration systems that can store thousands of litres of water. Most rainwater collection systems are comprised of the following basic components:

  • Catchment area is a surface from which rainwater can be collected. Roofs are the obvious catchment area. However, general paved areas such as paths, roads and car parks can be made suitable.
  • Gutters and drainpipes channel the water from the catchment area to a holding container such as a barrel, cistern etc.
  • Initial filtration removes or catches debris such as leaves before it enters the storage tanks.
  • Storage tanks can be above-ground or underground. Storage tanks can be constructed in a variety of materials and designs. To inhibit the growth of algae, storage tanks should be opaque and preferably placed away from direct sunlight. The tanks should also be placed close to the areas of use and supply line to reduce the distance over which the water is delivered. Also consider placing the storage at an elevated area to take advantage of gravity flow. The tank should always be placed on a stable and level area to prevent it from leaning and possibly collapsing. The size of the storage tanks is very important as the balance between the water volume that can be supplied and the demand for use of water needs to be considered. There may also be a requirement for a high-level header tank that is usually pump filled from an underground tank.
  • Delivery systems can be gravity-fed or pumped to the landscape or other end use areas such as a high level header tank.  All pipework carrying rainwater from the underground tank to the header tank and from the header tank to water fittings must be clearly marked as a non - potable water supply
  • Mains water top up is also required for the system in the event of a prolonged period with no rainfall.
  • Purification/treatment system such as UV may be required depending on the end-use.


Rainwater harvesting is not a ‘fit and forget’ technology. The following maintenance is required as a minimum:
  • Regular cleaning and maintenance and removal of debris collected is needed. 
  • For more sophisticated systems the following additional maintenance may be required:
  • Regular visual inspection of the system components and cleaning and replacement of filters and UV lamps according to manufacturer's recommendations is required. 
  • Ensuring mains water top-up is functioning and protected from contamination.

Safety Considerations

Storage tanks should have locking lids and/or bars that keep the children and pets out!

Please make sure that children and pets do not climb on the storage systems and accidentally fall into the storage tank.

It is important to ensure that there is no possibility of contaminating the mains water supply with non-potable water.

For more information

Irish Water Contact Details:

Web:  www.water.ie
Twitter:  @IrishWater
Telephone: 1850 278 278 (LoCall)
Minicom:  1850 378 378
(For hearing impaired customers with minicom equipment)
Postal Address: Irish Water, PO Box 860, South City Delivery Office, Cork City

Please continue to contact Dublin City Council for information or issues relating to business account queries, surface water drainage and flood management.