Supporting Wayne State University and University of Michigan’s flushing reminder

A recent press release reminded Flint residents of the advantages to flushing their plumbing and point-of-use (POU) filters.  We support this advice.

There are two types of flushing that are useful:

1 – Flushing out your pipes with your filter in bypass mode: Last year the EPA recommended that Flint residents flush their lines 5 minutes every morning to remove the increased bacteria that normally build-up in the water during stagnation, and to bring chlorine into the home.  The reminder to flush “several minutes” is consistent with this prior EPA advice.

2 – Passing your water through your POU filter for a short period of time to reduce bacteria, before collecting the water for cooking or drinking. The existing advice on how long to flush your filter varies. Some manufacturers have recommended 5 second, others 30 seconds, and still others including EPA recommend “at least 30 seconds” as illustrated in the following examples:

  1. “Flushing the filter for about 30 seconds after it has sat idle for several hours (such as in the morning) may help limit the amount of bacteria on the filter.”
  2. A high bacterial count can occur when water does not pass through an AC filter after it has not been used overnight. The first water drawn from the filter that day may be cloudy with bacteria. Flushing the filter at full flow for 30 seconds reduces the HPC bacteria counts to 1/7 the initial numbers, and as the AC filter is used during normal household activity for four hours, the HPC bacteria are reduced by 1/25. Still, several studies indicate that the HPC bacteria count is higher in effluent than in influent.
  3. These filters should be flushed for at least 30 seconds before each use.
  4. In view of these conclusions, it is appropriate to recognize that although bacterial growth occurs in POU and POE water treatment devices, the increase of HPC in these devices does not indicate that a health risk exists, so long as the water entering the device meets acceptable water quality standards. …Also, consumers should be instructed to run water at full flow for at least 30 seconds before use after a prolonged period of quiescence.

The Wayne State/University of Michigan advice to flush the POU filter for 15 seconds is, therefore, consistent with this prior guidance.