Installing a rainwater harvesting system can reduce mains water consumption by up to 50% in a domestic property, and even more in some commercial situations. That’s an attractive saving on commercial or household bills for your client. Compared against the initial investment of the system cost, a top of the range rainwater harvesting system will pay for itself, generate additional savings over the longer term and provide an ecologically sustainable solution.
Domestic properties will have different requirements to commercial buildings and the cost of the system will depend on a range of factors, including:
- The type of tank required for a specific location
- The tank capacity dependent on usage and collection area
- The size and shape of the tank
- The level of sophistication of mechanical and electrical components
What’s Included In The Cost?
The base components of a rainwater harvesting system include the filter(s), pump, storage tank, pipes, connectors, mains water back up and control unit. The UK Rainwater Management Association recommends that a quality domestic system should cost an average of £2,000 to £3,000, excluding additional features, installation and VAT. Commercial properties will require much larger systems, potentially involving additional features such as UV disinfection and monitoring units. Although the cost will be correspondingly higher, the return on investment is often faster and greater. When retro-fitting to existing buildings, additional costs may also apply to connect the gutter to the tank and the tank to the property.
Whether the system is being installed in a new build or integrated into an existing building will affect the overall costs. For new builds, planning may include an individual tank or shared tanks. There may be direct feeds or gravity feeds to each property. Excavation for an underground tank can be factored into new build plot preparation. For an existing building, excavation costs can be pricey, so check the likely costs with a building contractor before setting a budget. You’ll need to account for ground drainage and providing a concrete base for the tank. Other important factors are the cost of new conduit or piping to each utility, such as toilets and washing machines.
Calculating The Cost Of A Rainwater Harvesting System
Choosing the right system for the project will depend on the following considerations:
Tanks may be located above ground if excavation is not achievable. Above ground tanks will be exposed to temperature fluctuations, such as summer heat and winter freezes, so ideally should have some protection. Below ground tanks are the ideal where excavation is possible. Below ground tanks come in a range of capacities and heights to suit shallow or deep excavation, dependent on the space constraints and the type of ground.
The right tank capacity must be calculated correctly, based on yield and demand, with three key areas to determine:
- The geographical location of the property. Different parts of the UK experience widely different regional climates. For example, the North West typically receives heavier rainfall all year round than the South East. On average, it rains one in every three days in Britain.
- The roof surface area for rain collection – This is calculated by multiplying the length and width of the building, including any extensions.
- The number of occupants and the purpose of the recycled water – Will your client be using the harvested water for toilet flushing and garden use, or also for washing clothing? Consider how many litres will be required per day per person for each usage.
This information can then be used to calculate the most appropriate tank capacity to meet the requirements of your client.
Direct Fed Or Gravity Fed?
A Gravity Fed System requires space for a header tank in the loft. The water is pumped into the tank, where gravity provides equalised pressure to fill toilet cisterns or to feed appliances.
With a high-quality system, such as our domestic RainSava® or commercial RainTech® solutions, your client will benefit from low energy costs, as very little electricity is expended on pumping and the system standby power use is minimal. Your system cost calculation will need to factor in the price of the header tank. System prices depend on the capacity required, but a quote should take into account all the primary components required to make your system work at peak efficiency for the building and its occupants.
A Direct Fed System is appropriate for properties that do not have high level space for a gravity fed solution. When rainwater levels drop in the collection tank, a control unit will partially fill the storage tank with mains water, ensuring a constant supply; whilst complying with UK water regulations. Prices for standard domestic control units are relatively low, while a sophisticated system may cost you more. These typically include extra features, such as a leak detection alarm, suited to large domestic, commercial or industrial properties.
Value For Money
It is possible to source solutions below the price ranges recommended by The UK Rainwater Management Association, but you should consider the following points:
Guarantees – A quality system should provide long warranty on all mechanical components, management systems and tanks.
Pumps – An important component and the item that will receive the most wear and tear. For this reason it is important to use a high quality unit. Cheap pumps are cheap for a reason! Equally important is the pump controller; – beware that many have a high standby energy consumption, and since most of the time the system is in this mode, this can amount to a significant cost.
Support – There’s nothing worse than receiving components with no back assistance for installation queries and technical issues. Check whether the system is accompanied by telephone support, this should be a given.
Filters – No filter can remove 100% of sediment, but quality solutions will include features such as water inlet calmers, siphons and strainers to provide exceptional standards of filtration and clarity.
To summarise; the cost of a rainwater harvesting system is dependent on the quality of the components, whether the system is for domestic or commercial use and the size and location of the installation.
Whether your client chooses a simple rainwater storage facility for garden use, or a fully managed rainwater harvesting solution, each step towards reducing our ecological footprint is priceless.