Cost Benefit Analysis
for Graywater Systems
Return on Investment
Learn about the factors influencing your systems ROI (Return on Investment), in terms of avoided water bills, and other impacts.
Costs & Benefits
Reducing Water Bills
The average American water bill is $70.39 per month. Greywater systems can reduce a household's water use by 10% to 50%. A Greywater system from the laundry machine alone provides an estimated annual savings of 6,400 gallons per household. A common error is to assume that graywater production is equal to water savings. How much potable water-use you actually offset depends a lot on your design, the irrigation efficiency of your system(the % of total water applied that is converted for beneficial irrigation use) and the management of your sites water budget. The efficiency of different systems varies significantly (ie 15%-95% ), and many are installed in conjunction with new additional plantings which increase a sites water requirement resulting in a net 0 savings in water.
Cost of water likely to increase over time
The cost of potable water will likely increase in the future.
The major costs in maintaining and increasing water supply are: increasing operation and maintenance (O & M) costs, capital improvement projects, and the development of additional water supplies such as desalination and recycled water systems.
Costs of improvements to overtaxed water infrastructure are usually passed on to the customer.
Factors influencing ROI
System efficiency
More simple designs have a lower initial and operating costs and environmental impact (from embodied energy in manufacturing of materials etc.) but may not offer high levels of irrigation efficiency to offset spending on potable water. More complex designs that use drip irrigation may offset more potable water use/cost but may have operational costs (ie. electricity for pump) and a higher initial financial cost and environmental impact from high-tech components. Are the water savings sufficient to justify the proposed system? The answer is “It depends”, but cost/benefit analysis can also be drastically shifted in certain situations such as
failing septic system
Emergency water shortage
Large volumes of graywater
Low-tech systems are reliable, save water, and have lower initial costs (≈$500 - $4,000) and low to no operating costs. The fact that they don’t rely on high-tech components and electricity to operate means they have a low environmental impact and their overall net benefit is high.
Because high-tech systems are able to use drip irrigation and control the water to a high degree they have the potential to offset significant quantities of potable water use (irrigation water out of the tap), which over time could offer a high return on investment for the more substantial initial costs (≈$1,500 -$8,500) of a high-tech system.
Overall net benefit
is determined by summing all the “benefits” and subtracting all the “costs” of a project, referring to the overall impact a system has on your quality of life, water and resource use and ecological footprint. High-tech designs that use drip irrigation may offset more potable water use but may have operational costs (ie. electricity for pump), and a higher initial cost and environmental impact from high-tech components. Are the water savings sufficient to justify the proposed system?
