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I would like to build a fairly aggressive whole house water filter system.

However, the 1 micron filters that I see are low flow and are for point-of-use (under the counter for a drinking spigot) and are not appropriate for the flow an entire house needs.

I do, however, see many 5 micron filters that have sufficient flow.

If I cascade two or three 5 micron filters together, do they have an effective filtration that is actually smaller than 5 micron ?

Further, do two filters with the same flow rate maintain that same flow rate regardless of how many filters are in line ? I realize there might be a non-zero reduction in flow just because of the additional couplings, but I am hopeful that two or three filters, in line, with the same flow rate, maintains roughly that same flow rate.

Am I correct that I can get an effective 2 or 3 micron system with, for instance, three 5-micron filters in a row ?

Thank you.

  • You can increase the flow by using multiple fine filters in parallel, or a larger capacity filter. – fixer1234 Oct 25 '18 at 17:37
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No. If a filter allows a particle size to pass, more filters of the same porosity will pass the same particles down the line. As the first filter clogs, it may stop finer particles, but it will also impact the flow rate due to being clogged.

Multiple filters in line are typically either arranged coarser to finer, or are filtering for different things (i.e. physical and then chemical filtration.)

You can get more flow by using finer filters in parallel, or you can use a pressure tank after fine filters to provide a certain amount of filtered water at a high flow rate, before you hit the flow rate of the filter as the pressure tank empties.

Many high-volume water uses do not require superfine filtration - most notably in the average house, toilet flush water is an absurd thing to spend filtration effort/cost on.

  • Consumer filter micron ratings are averages, so a 5 micron filter sometimes lets through 6 and 7 micron particles and sometimes blocks 3 and 4 micron particles. But if I chain two together, my odds of stopping each particle double ... and so my average micron rating should go down - possibly below the rating of each individual filter. Right ? That is why I think two identical filters inline have a finer filtration than just one ... – user227963 Oct 29 '18 at 6:20

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