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This article outlines typical daily residential water usage in gallons for people, appliances, and activities. This permits estimation of wastewater volume (for septic tank size determination) as well as water and well flow requirements. Flow rates for common household plumbing fixtures and appliances is given.

This data is also useful when evaluating adequacy of private well and water supply quantity, well flow rate, and wastewater loads on onsite residential septic systems. Daily wastewater volume to be treated and disposed-of at a site determines the design parameters for onsite wastewater treatment or septic systems as well as suggesting choices among alternative septic designs and septic products.

We also discuss the effects of increased water usage when buildings use reverse osmosis (RO) for water purification. This document is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems. Also see The Septic Information Website

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Home and Outdoor Living Water Requirements, Plumbing Fixture and Appliance Water Flow Rates

How much water does a family use each day? What is the water flow rate for common household fixtures and appliances? The following table lists water usage requirements and typical fixture flow rates or device flow rates for home and outdoor living in the U.S.

Notes to Table:
(a) water flow restricting valves and shower heads can reduce flow and water use by up to 50%.
Source: USDA "Water Systems Handbook." (Thanks to Keith Oberg, Professional Home Inspection Service, Binghamton, NY, for providing this information.)
This data is used to estimate daily wastewater use in order to apply the septic tank sizing table located at SEPTIC TANK SIZE

Reverse Osmosis Systems - impact on septic systems and water use

What about water volume from reverse osmosis water treatment systems? These can vary by manufacturer with a range of 3:1 to 10:1 of waste to product efficiency. "Typically" for every gallon produced with a topo of the line system, 3 to 5 gallons goes into the septic tank. Less efficient systems (regardless of shutoffs) can dump up to 10 gallons to waste for every gallon that goes into the storage tank. Don't despair...the membranes of ten years ago dumped up to twenty five gallons per gallon of product.

For concurrence: ask the manufacturer for their efficiency, platform statement, and per cent recovery. An excellent resource for membrane information is the National Sanitation Foundation. I am not confident about the generalized information you obtain via EPA publications, Small Flows, etc. If you posture your inquiries with the reputable manufacturers, you should be able to get reliable flow information.

[Thanks to Larry Newcomb Encinitas Learning Center, jayhawk@cts.com, for the above opinion--DJF]

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More Information on Building Diagnostic Inspections and Repairs

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