Today is a special day for me… it was exactly a year ago when I first bought my own PUR water filter for converting my rainwater to drinking water, inside the trailer… On December 1st, I took the PUR filter apart to see what was inside… It was mostly filled with activated carbon, and at the bottom was a thicker filter that was folded in an accordion style, and fashioned into a circle for further filtration after the water left the activated carbon particles…

The PUR filter makers advertises that their filter will last up to 3 months and then the cartridge has to be replaced… but using rainwater, (instead of city or well water), the filter actually lasts only about 10 days before it clogs up… and so, three times a month, I had to replace the clogged filter with another $10 filter… it quickly became too costly to use the PUR water filter.

So, in December, (of 1998) I decided to make my own filter, which would be a lot cheaper… I found some Activated Carbon materials at the local Pet Smart store; Activated Carbon is commonly used in aquariums to refilter the fish tank water on a continuos basis… so I bought a large container of this carbon material and found a neat way to duplicate the PUR filter… I also added the second, fine partical filter to my filter, but replaced the PUR, accordian style filter with several layers of paper coffee filters and placed them on ‘top’ of the carbon filter to filter out sediments before they get to the carbon… The homemade filter still gets clogged by sediments up once a week, but it only takes 10 seconds to change out the coffee filters, so I think that filtering out the sedients before they get to the carbon is a good idea. I have also doubled the carbon used on my filter, and will soon increase it even more, to last me 6 months before I have to replace the activated carbon material… this homemade filter is simple, cheap, and easy to make… and the water output, looks good, smells good, and tastes good…

It’s been a year now of using my own rainwater filter, and this homemade filter has worked good for me… This morning, I was going to use my cell phone camera to take pictures of all the components of the simple and cheap, homemade filter, (to post them online), but alas, it has become very cloudy and dark… it seems that a new cold front is moving through this area and rain is expected for the next two days… so the pictures and construction information for making the simple rainwater filter will have to wait a few more days… By the way, as I finish this email at 11:27 am, Sunday morning, I can already see rain drops on the trailer’s bedroom window… so the rain is already started…

As you have discovered, a pre-filter for larger particulate matter is a very good strategy. Many systems use several, for increasingly small particles. I have seen this setup in many reverse osmosis systems, for example. Also, the most sophisticated whole-house filtration units do the same thing, often with filters that are quite large physically (perhaps a foot or more high). That said, activated charcoal itself is not necessarily proof against all biologicals, although those which are impregnated with silver help greatly on that score.

The most complete systems I have seen include a UV unit in addition to the particulate filters. Typical ones might have two or three progressively smaller particulate filters, followed by activated charcoal and the UV unit. Of course, this presupposes you have sufficient electrical power both for a decent pump and for powering the UV unit. Most of the UV tubes used for this purpose seem to need replacement annually, IIRC.