Flash floods, tropical intensity downpours and impending drought. No- one can deny, our climate is changing. Now the UK Ministry of Defence has ordered 150 Eco-Vat rainwater harvesting tanks costing half a million pounds each in the largest rainwater harvesting contract ever agreed in the UK.
Even the most conservative estimates anticipate that the temperature changes in the UK in the next decade will be dramatic. Sudden heavy downpours will increase the likelihood of flash floods and longer dry periods will lead to water shortages. Although there are no water restrictions currently in place in Britain, predictions this summer are for more record breaking temperatures, therefore it is part of national security to manage water responsibly.
The Environment Agency, planning guidance and Building Regulations all now include advice, requirements and legislation for the management of stormwater, to keep rainwater on site longer, to slow down run off and to use drainage systems that allow infiltration, attenuation (temporary storage) or reuse at the point of origin. As a whole, these systems are now well known as sustainable drainage systems – SUDS.
Rainwater harvesting; storing of rainwater for use in non-potable applications such as toilet flushing and garden irrigation, is one such system. A below ground SUDS option, it is a solution that could, with sufficient take-up, play an important part in managing our water resources. Commercial rainwater harvesting systems are also available, capable of serving anything from Schools to a large distribution depot. Enlightened specifiers are seeing rainwater harvesting as part of the SUDS package for all development types.
The design of modular stormwater storage cells offers great versatility, being lightweight and easy to handle, yet exceptionally strong. One type of modular cell uses columns of extruded polypropylene honeycomb structure, which can offer up to 96 per cent usable volume or void. This compares to around 30% for a conventional soakway (usually a rubble filled pit).
Unlike a rigid tank, a modular rainwater harvesting system can combine infiltration, or soakaway, with recycling, thereby alleviating the twin issues of water shortage and flooding. The other great advantage of a modular system is its flexibility; any size and combination of storage or infiltration unit can be constructed, just as long as room is allowed for the central pumping riser.
The new modular systems offer huge benefits over large tank rainwater harvesting options. A water recycling system can be constructed from separate components, using modular cells wrapped in impermeable membrane to store the water and other components to form a central filtering and pumping riser.
Rainwater is collected from the available roof area and passed through a silt trap before it enters another filter, where any fine sedimentary particles are removed. The filtered water is then fed to the base of the installation where it aerates with the stored water. The system can be connected to an outside tap, or used as a domestic backup system that can be connected via a storage tank to provide a supplementary water supply for non-potable applications.
Thew latest UK building standards make rainwater harvesting an integral part of all new home construction. According to the CSH, level 6, the highest level in the star rating system, is the standard to which all new homes, both private and affordable, should be designed and constructed by 2016, and it significantly raises the bar in terms of the environmental performance of residential buildings in the UK.
As standard, a level 6 house design needs to be completely net zero carbon. It must have zero carbon energy supply for space and water heating and all electrical power demand for the home, including electrical cooking and appliances. It must also be designed to ensure no more than around 80 litres of water is consumed per person per day. To achieve this level of potable water reduction, around 30% of the water requirement needs to be provided from rainwater harvesting or water recycling systems.
In order to achieve a level 6 house, the thermal performance and airtightness of the building fabric must be maximised, building services must be integrated to optimise efficiency and a comprehensive platform of renewable and sustainable technologies must be incorporated into the house or development design.
The MoD order is worth