When wrong, yet simple, math costs water customers money

Is the state’s required calculation method costing your water system thousands of dollars?

For many small and rural drinking water systems, the answer may be yes — and it comes down to how “average” is calculated.

The State Division of Drinking Water requires a simple average to determine long-term arsenic levels as well as other contaminants. Madera County simply follows the state method.

While straightforward, this method can produce misleading results — sometimes overstating contaminant levels far beyond what customers actually receive, and falsely resulting in requirements for costly remediation.

In our small mutual water company, the simple average method incorrectly calculated that arsenic level was more than three times higher than the actual concentration delivered to customers.

That difference meant the county classified our system as out of compliance and potentially requiring costly measures. These costs fall directly on our customers. The falsely calculated high concentration level also creates unwarranted public concern.

A more accurate approach is weighted averaging, which accounts for variations in water flow over time. For those systems that have variable production levels, a common situation, this method better reflects actual water quality.

Using it, our system, Sky Acres Mutual Water Company, is clearly within allowable limits.

So why isn’t it allowed?

State officials insist on simple averaging, hinting that the legislature wants high quality water and simple averaging helps achieve that. But the calculation method does not change the water quality.

Further, no regulation explicitly requires it or prohibits weighted averaging. Federal EPA guidance already allows flexibility, leaving the choice to the state.

This is not about lowering standards — it is about measuring compliance accurately. When flawed calculations drive decisions, communities may spend thousands solving a problem that does not exist.

It is time for the State Division of Drinking Water to allow methods that reflect real-world conditions and ensure decisions are based on sound data, not outdated practice.

If you would like more information, or would like to join us in this effort, please contact us at SkyAcresMutualWC@gmail.com.

Heather Taylor is treasurer and Dan Metz is president of , Sky Acres Mutual Water Company in Oakhurst.