Newhouse Farm

[Chaz]

As my well water is collected in my outside 1520L storage tank is there something I can hang in the water to kill bacteria etc rather than using an in-house very expensive UV filter ?

Inside my home the water comes in via a sediment filter and PH/taste & odour filter into a pressurised pump system with a seperate tap/filter for harmful cysts, not that I've ever had a problem in the last 20 years but better to be safe than sorry.

Any suggestions welcome,

Thanks,

Chaz

[Mike&Penny]

Filtration works.

Some useful ideas.

1) Don't try to do it all in one step. That's expensive (or time consuming rebuilding if homemade "slow sand"). Use a series of fliters going from coarse to fine so that the fine filters aren't clogged by material the (cheaper) coarse filters could have removed.

Thus if using commercial filters, perhaps 20 micron then 2 micron then 0.2 micron (the last won't let any "critters" through, even stop some of the larger viruses)

2) If the pressure drop is too great, remember that you can reduce that with filters in parallel. Those would all be the same fineness and you would probably want to replace as a set to keep the flow reasonably balanced.
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There is no possibility of social justice on a dead planet except the equality of the grave.

[Studentmum]

Sorry to hijack the thread but what are your grounds for stating that no "critters" will get through a 0.2 micron filter Mike&Penny? That is only true if they are
Other than that, Chaz - under normal conditions 0.2 micron should be fine. Ozonation could be an option but quite expensive I think

[Mike&Penny]

An explanation (why it is so -- why filters work in practice)

When people express concern that a long needlike organism with smallest dimension N could easily pass through a filter membrane with pore size M (M greater than N) they misdraw the picture. They draw for you a "wall" of thickness P with P much smaller than M and suggest that the needlelike organism with diameter N could easily slip through.

The error in that picture is in drawing that wall with thickness P less than M. In reality the filter wall with pore size 0.2 microns might be a millimeter or more thick. In other words, that wall is thousands of times thicker than the pore size and what you have isn't a "hole in a wall" but a very very long and in all likelihood not very straight tunnel. Hard for that needle to pass through without jamming somewhere along the way (why the filter will eventually "clog" and need to be replaced).

Picture the difference between trying to fire a bullet through a 1 meter diameter hole in a board fence from a distance of 10 meters and trying to get that bullet through a kilometer tunnel that diameter (ignore gravity, just consider the acuracy needed in aiming if there were no gravity and the bullet would go perfectly straight).

BTW -- this is why the kind of filter I use in the wild comes with two fineness designations, "absolute" and "effective". In other words, the physical pore diameter (absolute) is 0.4 microns but when tested with dye particles 0.2 microns in size those can't get through in practice. These are roughly ball shaped particles of that size and so smaller than almost all organisms of ball shape. There are indeed organisms shaped like needles with diameter smaller than this but length at least a micron or two. That shape gets jammed easily at the slightest bend. In our area of the world the organism backpackers need to worry about is giardia ("beaver fever") and the cysts of this organism are about as needle like as they come. But very few will pass through even a 0.5 micron effective filter.
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There is no possibility of social justice on a dead planet except the equality of the grave.

[Studentmum]

Thanks for taking the time to post that - very enlightening!

[Chaz]

Many thanks for your suggestions, Mike&Penny and Studentmum, much appreciated.