The pond filter has been running for about 7 months now. It has frozen solid twice, however it did thaw out both times and it is still working. The most recent test showed less than 2 coliform bacteria per 100 ml of filtered water taken from the output of the filter. The most recent occurrence at the pond was a swimming event enjoyed (I presume) by raccoons. The water was full of mud, and the pond looked like a mud puddle with the water mostly opaque brownish-green. This type of event happens regularly. The leaves and other decayed organic material had clogged the pump and the water was just barely circulating. The raccoon event resulted in the loss of the fish that were in the pond. After cleaning the little pump and testing the flow, the filter was running again. Within less than 24 hours the water in the pond was clear.
The sand has settled on the bottom and the rest of the nasty stuff in the water has been removed by the filter.
Now, why is this significant? Why am I even bothering with this? Well, this is actually an experiment to determine if it is possible to put together a working slow sand filter with very, very coarse sand (.45 mm effective size) and only a flat rock inside as a baffle. The answer is yes. Now, I would not recommend drinking this water, but it would be acceptable to use it to water a vegetable garden, or to do laundry with, or just about any use except drinking – but this filter is cleaning water that is extremely contaminated – far more than any source a person might use for drinking water such as roof water or water from a shallow well which would not contain mud, nor have critters wallowing around in it. So the next step will be trying a similar set up with water that is reasonably non turbid to start with and only moderately biologically contaminated, such as roof water. . . more later.