Does the System Have a Problem? You Better Know the Flow.

If you’re not monitoring water usage, accurate analysis of system performance may be just a shot in the dark.

Does the System Have a Problem? You Better Know the Flow.

Jim Anderson, Ph.D., is an emeritus professor at the University of Minnesota Department of Soil, Water and Climate and recipient of the pumping industry’s Ralph Macchio Lifetime Achievement Award. Email Jim questions about septic system maintenance and operation at

Afew months ago, I wrote about new research done on residential water usage and how changing the estimated daily water use can impact system design, including septic tank size and soil treatment and dispersal area.

The research showed a decrease in average water use by a household from the previous estimate of 75 gallons per day per person. But questions remain whether this should result in changes to water use estimates for design purposes. The 75-gpd estimated water use per person was based on the flush toilet using 5 or more gallons per flush. Now the federal plumbing standard specifies the use of no more than 1.6 gallons per flush. Some toilets use a little as 1.28 gallons per flush.

I received a few comments and wanted to share them to promote additional discussion and, perhaps, give designers and regulators some ideas for different approaches.


One reader responded that in their area, house ownership changes on average every 10 years or less, leading them to purposefully “oversize” systems to avoid problems in the future. If oversizing was not possible, additional pretreatment was added to improve system performance.

While this approach could be followed, it should be recognized that average design estimates of 450 gallons per day for a three-bedroom house already have a level of oversizing built into them. The reader did not explain how systems are oversized, but if additional treatment area is added, this may be an unnecessary expense for the homeowner and something they will never use. Adding additional pretreatment can be a good idea to improve system performance, yet it may not be necessary.

I can only assume they are using these approaches after being “burned” by system failures due to what they perceive as changes in water-use patterns when a house changes hands. Water use may or may not be the problem. The problem could be flawed soil analysis or soil compaction during installation, resulting in the soil not accepting the amount of effluent expected. Or it could be a combination of all of the factors mentioned above.

Another reader says it’s unfortunate that the onsite sewage industry, designers and manufacturers have not routinely used water meters to evaluate existing systems and to make decisions about increasing system size when additional people occupy a home.

Water meters installed to measure flows to the treatment system would make identifying problems and size decisions much easier. In addition, over time there would be a record of water use to compare with drainfield performance, providing a better picture of how much effluent the soil will accept.


Installing a household water meter costs roughly $200 to $250, which seems to be a small price to pay for information that can help the homeowner and service providers make sound decisions about managing systems for long-term performance.

If a water meter is installed every time a system is repaired or replaced due to failure, or increased in size due to additional occupants, service providers and regulators will have the information needed for accurate system sizing. It would take the guesswork out of the first reader’s approach to make everything larger.

The same reader commented that use of new distribution media should trigger water meter installation and laying out the system in a manner that allows for evaluation of actual system use. The reader notes seeing numerous system demonstrations where there was no way to evaluate how well those systems work.

I agree that a lot of sizing decisions have been made by state and local regulators and service providers without adequate information on water use. This has led to a lot of head-scratching and wondering why something appears to work in one place and not another. Having accurate water-use data can answer a lot of those questions.

Before leaving this subject, I must say that I am encouraged by what I see happening in the industry lately in this regard. A number of proprietary products have built into their systems the ability to measure water flow through the system along with a way to measure soil performance. In addition, products on the market can be retrofitted into existing systems to measure flow and soil performance. These products, if adopted and used by service providers, will provide a true picture of system performance, leading to better management. This ultimately provides the homeowner with a system they can have confidence will accept and treat their effluent indefinitely into the future.


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