How long will a slow sand filter “run” before it needs “repair”?
This is a good question. This blog has 8 years of posts documenting the slow sand filters running here. I can say with certainty that the longest running filter here (filter 1) is still fully functional after 8 years of continuous running (with the exception of several weeks each winter when all the filters freeze up and stop running). In filter 1, the sand has not been changed and the filter has not been wet-harrowed; and no sand has been removed or added. Recirculation is used in the summer when little or no rainfall occurs.
The other filters running here have been in continuous service for various lengths of time. Anywhere from 5 years to 8 years. All filters, with the exception of the 5 gallon filters, and the smaller 1/2 gallon filter, are still fully functional and currently in service. The 5 gallon filters were not successful, and we have stopped working with them. The smaller 1/2 gallon filter was never fully tested thoroughly enough to show any success.