I spoke with the testing lab this afternoon regarding filter 4. The filter is working. “Working”, means that the filter is removing coliform bacteria completely from the input water; however a word of caution here: this is only for this filter at this location and is only one test. It must be kept in mind that contamination can come from anywhere and each owner is solely responsible for the operation of the filter they build and/or own. It is totally possible to build a filter identical to this one and have bacteria show up in the output at any time. Also note that the “log reduction, (usually called “log credit”) on this filter has only been shown to be 3.08 with 1200 cfu/100ml input. This means that unless the water running through this filter is equally or less contaminated than 1200 cfu/100ml the output may be toxic.
For example, let’s say the water coming off the roof suddenly has 2000 cfu/100ml (this can easily happen anytime – contamination levels in roof water will vary SIGNIFICANTLY) ; then this filter may not work to remove all the pathogens. Or, perhaps someone else builds an “exact copy” of this filter and starts running their roof water through it. There is absolutely no guarantee that the filter will work – it “might” work. There is no way to tell. It might produce horrifically toxic water. A test must be done on each filter, and furthermore, the water should be tested and monitored regularly with adequate safeguards for possible contamination. Even if a UV filter is used, if the turbidity goes above the limit for the particular type of light, then it will not inactivate pathogens, so the turbidity level must be monitored closely also. This filter has not had a turbidity test done yet.
The results are:
Post-filter: no detectable coliform, this means no e coli or fecal coliform are in the output water.
Pre-filter: 1200 cfu/100 ml.
Storage: 3 cfu/100 ml. no e coli or fecal coliform.
The results can be viewed here: http://www.roofwaterharvesting.org/test_results.html
Specifically, this means that water directly out of the filter has no detectable coliform bacteria in it. Water that has been going into the filter on an ongoing basis has a high coliform count, and water from storage is slightly contaminated with 3 coliform per 100ml but contains no e coli. This does show that contamination can come from anwhere, as I had meticulously and extra carefully cleaned out the storage container with disinfectant and made sure the container was closed tightly. Still, from somewhere some coliform has managed to get into the system after the filter output. However, inside the filter at the output and inside the output pipe there is only purified water. The actual paperwork will be coming back to me in several weeks at which time I will post it online.