Rain Water Harvesting
What is rainwater harvesting?
Rainwater harvesting is a water conservation system designed to store the rainwater that falls on a roof. The system works by transferring the rain water that is collected by guttering through a filter and then into to a large storage tank. This storage tank is often buried in the ground next to the property.
This tank typically has an electric pump that pumps the water into your domestic home or commercial premises to be used for your toilets, washing machines and even drinking water.
When the system is correctly specified it can provide up to 50% of the annual water requirement for a domestic home
The benefit of using the rainwater that falls on your roof is that it enables you to reduce your metered water bill and save the energy involved with purifying and pumping of the water delivered by your mains connection. The planning regulations for sustainable homes is also adding additional pressure on developers to utilise this type of equipment.
Did you know?
• Only 0.4% of the water on earth can be used as drinking water.
• The average household uses over 500 Liters of potable water per day.
• Water conservation Directives from the EU mean that pay by use water charges are inevitable.
• The average rainfall in Ireland is 1100 mm per year with the lowest rainfall in the southeast and the highest in west and northwest.
Who should be interested in rainwater harvesting systems?
The most common use of the stored rainwater is for toilets and washing machines this means that a typical property has a separate cold water system for drinking water and for rainwater. Self builders and developers are best positioned to utilise this technology as excavation and plumbing works can be integrated into an existing project extremely cost effectively. Retrofits are also a viable option where there is the facility to connect into the existing plumbing system or where there is a demand for water for non domestic applications i.e. gardens, car washing etc
Does rainwater harvesting make sense more for commercial or domestic premises?
Both domestic and commercial properties can benefit from rainwater harvesting systems. However commercial properties often have large roof areas and a high demand for toilet flushing, fleet vehicle washing and site irrigation.
This means that while a domestic installation can provide up to 50% of the water requirements, a commercial property could utilise considerably more rainwater
How it works
The Rainwater Recovery system (R.R.S.) is a unique environmentally proactive system designed to reuse rainwater. The rain is gathered, filtered and purified, then pumped to your attic storage tank for use. RRS is ideal for businesses who pay water charges and for those who are concerned about the use of natural resources.
The Process:
• Rain water is gathered from the roof of your house using the existing gutter and down-pipe.
• The down-pipe is connected to a storage tank.
• When the water level in the tank reaches a suitable level a sensor activates the RRS.
• The RRS then filters the water to remove any impurities before pumping it to the attic storage tank.
• When the system is activated you regular water supply is shut off. Your main supply will be reactivated when the down-pipe storage tank is empty.
Water capture and storage systems: general principles
The key issues for rainwater capture and are:
• Source
• Treatment methods
• Storage
• Collection and distribution pipework.
The source of the rainwater should be taken into account when deciding on a system that is the size of the roof area the location of the built and the annual yearly rainfall should be calculated in advance to determined whether the project is feasible.
Treatment processes are associated with most of the operation and maintenance requirements in order that the collected rainfall may be suitable for use.
Storage requirements are calculated with regard to the level of consumption and the frequency of supply. Rainwater tanks are sized to provide a continuous supply between rainfalls, typically 12-20 days.
One of the issue associated with the collection and distribution network involves the avoidance of any risk of contamination of the mains water system. This is normally provided for by means of backflow protection, another consideration in the design of the distribution system is avoiding deadlegs in which stagnant water might collect. Infrequently used facilities, such as guestroom toilets, are better served using mains water.
Special considerations: rainwater capture
Rain provides water that can supply toilets, irrigation systems and appliances such as washing machines and dishwashers. The quality of the water is determined partly by location and also by the nature of the catchment – for example, exposure to forms of air pollution or potential contamination from bird droppings. Most roof materials are suitable as catchments, as are permeable pavements.
Filtering is a key element of the rainwater capture system. Depending on the end use, several stages may be required to achieve an acceptable level of quality and to protect pumps and other systems from excessive wear. Automated cleaning processes and easy access to the filters for inspection and replacement is vital to ensure the long-term performance of the system.
The design and specification of storage tanks introduces the following issues to be considered:
Tank sizing:determined by a combination of the water requirement, rainfall patterns and the available catchment. The extent of the catchment is determined by downpipe routing or, in SUDS, through the use of impermeable barriers to isolate a section of paving.
Tank location:finding enough space to accommodate a tank that can hold the intended water capacity. This can be a significant issue for communal systems and an underground tank may need to be specified. Underground tanks introduce a range of issues related to loadings, movement, and flotation and so on. Underground tanks also need ventilation and must be kept safe from contamination from floodwater in the event of severe weather.
Access:providing easy access for inspection and maintenance is important if long-term water quality is to be maintained.
Standards:
• The rainwater recovery system complies with the EMC electrical standard.
• The system is also CE Marked.
Filtration:
• The rainwater recovery system uses two particle filters as well as a UV filter to ensure water is of the highest quality.
Control system:
• The unit is controlled by a programmable logic controller that is preset in the factory to activate the system when it rains and automatically re-establish the mains supply when the rainwater has been used.