Rainwater Harvesting Advice
Rainwater harvesting experience in the UK is growing fast, however, the current best practice comes from Germany. The German industry has 15 years more experience and a significantly larger market. Ecozi will assist with detailed design and product specification for each system.
General Advice for all Systems
- the rain yield for the roof area must be respected. If not enough rain is available for the application demand a part-building system should be installed. Part-building rainwater harvesting systems will be more efficient with reduced electrical power consumption and will operate 80%+ of the time with rainwater
- only connect roof drains to the storage tank. Car parks and other hard standing areas should not be used in a rainwater harvesting system due to the increased risk of contamination from animals and hydrocarbon spillage
- when connecting down pipes to drains at ground level use sealed components only with no traps, gullies or bottles. The piping network acts as an air vent to the storage tank and surface ground water should not be able to enter the system
- underground storage will provide the optimum conditions for water storage. Above ground storage will increase the risk of bacteria and stagnation
- do not install a tank larger than your roof can support or larger than your demand. Doing so may lead to a reduction in water quality as the skimming effect at time of overflow will not occur regularly enough
Which system is right for our project?
Residential systems for a family of up to 4 people require a 3,500L tank, nearly always with an internal filter and a residential wall mounted management appliance. For homes without a suitable location for the integrated control unit, a pump-in-tank system is available. Small commercial schemes require larger tanks, filters and wall or floor mounted management appliances. Large commercial schemes can require bespoke design and 6 week lead times for high performance products. In difficult ground conditions precast concrete tanks are required. For system redundancy multiple management appliances can be used and/or hybrid pumping systems with multiple parallel pumps operating as the demand requires.
How easy is it to install?
Skills required are drainage, plumbing and pump commissioning. Excavation works for the tank installation will require at least a 3 ton machine to enable a 2.5m deep pit for a private dwelling. The two trades’ people that commonly install systems are ground workers for the tank and drainage and then plumbers for the first and second fix.
What is the payback period (ROI)?
For a residential system the current payback period is about 15 years based on the product cost. A commercial system payback can be as low 3 years. Each application is different but large roof areas enable large volumes of water to be captured. High demand applications and large roof areas provide the shortest payback. Rainwater harvesting offers one of the shortest payback periods when compared to other sustainable technologies.
Why should I specify an Ecozi system?
Ecozi will support the rainwater harvesting system designer/specifier at an early stage and share industry best practice. Using a single German producer for 80% of our systems provide reassurance that all the components are matched and designed for optimum performance when used together. Ecozi uses ASP-UWO products who have been producing rainwater harvesting systems since 1990.
What support can I expect from Ecozi?
Ecozi only markets rainwater harvesting systems and has built up expertise for all applications. Detailed manuals with photos provide reassurance to self builders and M&E contractors alike. Telephone advice before, during and after installation is available at all times to all customers. Commissioning services can be provided at additional cost but are not necessary unless you are installing large scale commercial systems. Ecozi staff aim to ensure all aspects of the design have been considered before acceptance of order.
What type of technology is best?
Hybrid technology for commercial systems involves the use of multiple pumps that efficiently alternate as the demand changes. Direct pressure systems offer the lowest installation costs and ongoing maintenance with excellent performance from high pressure pumps. Use of the best systems will avoid submersible pumps and the associated problems with maintenance and access.
How quickly can you supply a system?
Tanks up to 6,000L are stock items, as are filters for roof areas up to 500m². Residential and small commercial management appliances are also stock items. This means complete assembled systems can be shipped to site in just a few days from receipt of order.
When should I install the Rainwater Harvesting System?
The tank can be installed at either initial groundworks phase or after the scaffolding comes down and the drains are finished. The management appliance will be installed at second fix but rainwater harvesting plumbing to the appliances needs to be installed at first fix. It is important to install a DN100 duct (or larger for commercial systems) through the footings with shallow bends up through the floor at the location in the building where the management appliance will be located.
What is unique about Ecozi systems?
Ecozi focuses on direct systems with factory built appliances enabling simple and fast installation. End user maintenance is reduced and whole life costs are lower. The PE and PP tank ranges have smooth internal surfaces that are easy to clean during long term maintenance. Using high performance multi-stage pressure pumps built into factory assembled and tested appliances long term reliability is assured and the need to enter the tank for pump maintenance is eliminated.
What applications can I use rainwater for?
Toilet flushing, irrigation, vehicle washing, non hygienic cleaning, laundry (not commercial, or in schools or hospitals or care homes) some industrial processes and increasingly fire extinguishing equipment and building cooling systems.
What quality standards should the system meet?
The system should be designed, built and supplied from known parties. Long life systems will rarely be the lowest initial cost as they will use premium pumps, valves and control components. Installation does not require any unique skills it does require care and good knowhow to install reliably and meet all best practice.
What grants or funding are available?
For commercial businesses, rainwater harvesting qualifies for the Government ECA scheme. There are no direct subsidies or grants for rainwater harvesting for private projects. From time to time local Councils or Government agencies may offer specific conditional grants.
What surfaces can I connect to the storage tank?
Only roof areas that cannot generally be accessed by people or animals should be connected to the rainwater harvesting system. Driveways or other hard standing areas are not suitable due to the risk of hydrocarbon or faeces. Open gullies or traps should not be used at the point of intersection with the downpipe and underground drain.
What regulatory requirements are there for rainwater harvesting systems?
There are currently no direct building regulations for rainwater harvesting. However, drainage is covered by the Building Regulations and can influence rainwater harvesting system design such as soakaway or city drain connections for tank overflow. Several other associated regulations apply; In England and Wales the Water Supply Regulations 1999 (Water by-laws 2000 in Scotland and Water Supply (Water Quality) Regulations (Northern Ireland) 2002) must be adhered. These regulations are enforced by the water supplier. The essential requirements of the regulations specific to rainwater harvesting are; (1) no cross bonding of rainwater piping with potable supply pipes (2) prevention of backflow to potable water supplies according to CEN EN1717 with air gaps (3) the clear marking of rainwater pipes according to WRAS # 9-02-05 and (4) material specifications, where contact with wholesome water is permissible meet the prevailing approved list.
Is rainwater harvesting technology new?
In the UK, the first early adopter systems were installed in the late 1990’s and were bespoke designs. Ten years earlier, in the late 1980’s the German market was created with rising water prices and a greater environmental awareness. Regional Government grants started appearing too and the market grew rapidly. The best practice and advanced designs can be found in the German built systems.
What are the maintenance requirements?
Regular, simple filter maintenance is required to make sure the filter is not blocked with debris. Blocked filters have a significantly reduced efficiency and most rain will be wasted. Other system components need to be visually checked for deterioration every 9 months. Replacement parts would not be expected for at least 10 years. Every 7-10 years the tank will require draining and the internal surface cleaned.
What is the cost of installation?
The lowest costs are achieved with a new build. Excavation works for the tank are additional requirements as is a plumbing network for the rainwater appliances and commissioning of the control appliance. Other works such as drainage and soakaways have to be completed with or without rainwater harvesting. The incremental cost to install a rainwater harvesting system for a private house should be around £700. A commercial system will have increased excavation costs for the larger tank and internal plumbing costs depending on the number of toilets/applications.
Can I use an above ground tank?
Commonly for retrofit systems an above ground tank is the first thought. For some applications this is OK but the main problems are quality of water and drainage connections to enable a large enough roof area to be captured. The ambient air temperature will enable bacteria growth inside the tank that will lead to smell and a faster algae build up inside the tanks. If the water is for irrigation or washdown the quality could be acceptable, however, for toilets this is unlikely to be the case. For an industrial building it could be possible to hang horizontal drain pipes on the cladding to enable enough roof area to be connected to the tank. Office buildings and buildings with aesthetic considerations will have difficultly connecting enough roof drains to the tank.
Can I use a gravity fed tank inside the building?
Theoretically yes, but such systems are hard to achieve in reality. If a tank can be positioned inside the building higher than the highest toilet with rainwater collection directly from the roof then use of a pump could be avoided. The building will require special design to achieve this. The quality of water will be poor due to the warm storage temperatures relative to the 8 - 10°C year-round when underground. Water stored in these conditions will diteriate quicker, can smell and algae growth will occur much quicker inside the tank.
What is the best architecture for a commercial rainwater harvesting scheme?
In the advanced and mature German rainwater market hybrid systems have appeared over the last 5 years. These systems have been designed from experienced gained in the largest rainwater harvesting market. These systems seek to achieve the best water quality with ease of installation and low maintenance. The heart of these systems is a floor mounted management appliance that is factory built and tested eliminating manual wiring of controls systems and concentrating all main components in the same appliance. The management appliance has an intermediary tank with 2 (or more) pressure pumps to directly feed toilets and applications calling for demand. Rainwater from the main underground storage tank uses a lift pump (no pressure) to feed the intermediary tank and the mains water backup also feeds the intermediary tank when required. This architecture means that only a loading pump is located in the main underground tank and all other items in the control system are appliance based. The need to enter the tank or even work at the tank access area is all but eliminated. The water quality is very high and process logic can be applied for different fault conditions to provide the highest level of appliance service time.
What size tank does my project require?
Ecozi will make these calculations for you but best practice is usually based on a tank size of 5% of the lower of the two annual figures of (i) rain available (from the catchment area) and (ii) rainwater demand (from the applications and number of occupants) .
What material is best for the tank?
Small tanks, up to about 12m³ are usually single skin 12mm wall polyethylene (PE) suitable for underground use in most applications, without concrete backfill. PE tanks are light weight and super smooth on the inside minimizing algae growth enabling 10 year cleaning cycles. For larger tank capacities, tanks in poor ground or high surface loads precast concrete are best.