Why filter perfectly good water?


By Greg Illes
Why filter perfectly good water? The answer to that question is another question: How good is “perfectly good”?

Many RVers use the water that the RV park supplies, straight from the tap. After all, that water comes from treated sources and should have no problems. Right?

Well — maybe. Yes, it’s reasonable to assume that a typical chlorinated municipal supply is biologically safe. But that’s only guaranteed at the water treatment plant output. The distribution system can be full of flaws that degrade the quality of the water before actual use.

And that’s not to mention if the local water is coming from a private well, with something subtle in the treatment protocol not working properly. UV irradiation bulbs burn out, filters get clogged, etc.

Aside from health issues, rust and sediment are the biggest culprits, and they increase with the age of the distribution system. The photo shows a graphic example: a new ceramic 0.5um (micrometer) filter, and a second one with only a few hundred gallons through it. It was so clogged with rusty sediment that the flow had slowed to a trickle. It had never been used anywhere except from certified sources.

Odors and tastes can be “safe” but still objectionable. A friend’s house, in another town, provided municipal water — with a noticeable “stink” when it first came out of the faucet. Nobody got sick, but it wasn’t pleasant.

Bottom Line: When I fill my motorhome’s fresh water tank, I would like to be certain that the next 75 gallons of water I drink, shower with, or use for cooking, is going to be good for my equipment, and good for me.

But such certainty is a real challenge. I can’t possibly test for contaminants and parasites every time I need a fill. And I can’t have every single possible filtration and treatment protocol (there are dozens) applied to all the water I take on.

The answer, as with so many things in life, is a compromise. With properly treated water as a baseline, I have settled for a simple configuration: a fairly fine-pore sediment filter, augmented with activated carbon. The fine-pore filter removes all but the tiniest particles of sediment and screens out any nasty protozoans that might have crept in (e.g., giardia, cryptosporidium). The carbon takes out any odors and tastes. For me, this is an acceptable balance between trouble/cost and quality/safety.

In order to keep an eye on my filter’s health, I chose a clear whole-house housing like the Pentek 150071 (shown). The business of actually doing the filtration is handled by a special high-flow cartridge like the Pentek Flo-Plus, which has great flow performance even with fine (0.5um) filtration. I would hate to have great water at the cost of an hour’s wait to fill my tank. (Not to mention holding up the people in line behind me.)

I screwed pipe-to-hose adapters into the housing so that it could be connected right at the source faucet — that way, I don’t let any “strange” water into my hoses or fittings.

YMMV (“Your mileage may vary,” for those who don’t know) — Note that different people (preferences, allergies, etc.), different water, locales, and use demand different solutions. What works for me might not be your best or safest choice. I’ve only outlined my configuration here by way of example, and not as advice. I’ve seen people with dual-filter setups, UV-light setups, silver-impregnated cartridges — the list goes on. Some folks don’t bother with filtration at all. Some people boil every drop that they drink. It’s up to each individual to sort out their own best approach.

Please feel free to leave a Comment about your own “adventures” with water, and your own filter solutions. We can all benefit (and often be entertained) by each others’ experiences.

Happy travels, and safe and healthy living as well.

Greg Illes is a retired systems engineer who loves thinking up RV upgrades and modifications. When he’s not working on his motorhome, he’s traveling in it. You can follow his excellent blog at www.divver-city.com/blog .



13 Thoughts to “Why filter perfectly good water?”

  1. Roy Ellithorpe

    I have installed reverse osmosis in our last 2 rigs, and we drink the water from everywhere including Mexico. I only have the RO water supply the fridge for ice and drinking. I’m not a total whacko environmentalist, but I do dislike waste in general, so the massive amounts of water that the RO wastes is diverted into our fresh water storage tank and periodically I turn off the city water and turn on the pump in the morning for showers.

    1. Steve

      Interesting idea, but the reject water from the RO system would be very high in contaminants and all the other stuff the system filters out. I would be concerned that this water would have negative effects on valves and such.

      Or am I barking up the wrong tree?

  2. AdamK

    Drain the cartridge as best you can – put it in a Ziploc bag and then in the freezer. Freezing it will not allow any bacteria to grow. I do this with folding water bottles too as the insides are very difficult to dry completely.

  3. Irv

    How can I keep my carbon filter cartridge microbially safe during 6 week periods when the RV and filter are not in use?

    Pentek CFB-PB10 Lead/Cyst Filter-10″ Carbon Filter

    I tried dipping the cartridge in a bleach solution and then putting it in a dehydrator for several days until its weight dropped to that of a new cartridge (indicating it was dry).

    My idea was that storing it dry would prevent microbial growth but it’s not worth the trouble for a $13 cartridge.

    My current plans are to replace the $13 cartridge after every trip. Any better ideas?

    1. Greg Illes


      Honestly I haven’t given that topic much thought.

      If you are truly concerned, I agree that replacing the cartridge is the best bet. But it does beg the question: How long a period (leaving it stored and damp) before you have to worry? Weeks? Months?

      Let us know if you find some good info on this.


  4. John Snell

    I have a pull behind trailer . Is there a filter I can attach to the hose for the city water. I get the concept of filtering on board tank for drinking or cooking and using city for other uses.

    1. Greg Illes


      All of the RV-specific filters have standard hose-thread fittings and are simple to hook up.

      If you want to use a generic filter (like a whole-house), you’ll have to take it to a hardware store and get adapters to go from pipe-thread to hose-thread. Pretty simple.


  5. Mike Bacque

    We also use a two filter system no matter where we’re hooked up or fill our water tank. Nothing goes into our unit unless filtered. We have a third filter on our drinking water faucet at the kitchen sink. Too many communities have had water issues over the years to not use some type of water filtration. As an example, we arrived in Corpus Christi last December to a water scare due to the possibility of an industrial back flow into the water supply. Turned out to be a false alarm. Phew…

  6. Juan Camacho

    We have an in-line Camco filter that filters the whole house, so when we’re at an RV park with full hook ups I take the out door shower faucet off and stick the hose in the on board water tank. 100 gals takes awhile but all the water first goes thru in-line filter.

  7. Lyle

    My setup is two sediment filters (5 micron to a 1 micron) then to a bacteriostatic carbon and lastly through a water softener. Several years ago we just used one of the online Camco filters and the campground stained our toilet. Our dogs wouldn’t drink the water either which was our first sign water might be bad.

  8. Tommy Molnar

    We’ve been doing fine with just one filter setup for 20+ years – until we took our first trip to Quartzsite, AZ. Within less than a week our toilet got clogged with calcium and would barely flush. Twice I had to completely take the toilet out and ‘pick and blow’ all the fittings out so enough water would flow and flush as advertised. So now I’m on the hunt for SOMETHING to remedy this problem (short of reverse osmosis which wastes too much water). Maybe two (or more?) filters? Gasp! We love going to the Quartzsite area so not going is not an option. I hear this water problem is an Arizona problem, so I guess it’s not just the Quartzsite area.

    1. George

      There was (and maybe still is) a place in Quartzsite on the east side of hwy 95, that has deep well water. It cost $5.00 to fill my tank and every container I could muster up. That was 5 or 6 years ago and I don’t know if they are still there. It was a big lot that could handle several large RVs at one time. After 8 winters in AZ, mostly Yuma, we’ve never had an issue with clogging pipes, but we do run off the city water system in Yuma which is undrinkable because of the salty taste.

    2. Tom Fikes

      For Quartzsite, and almost anywhere else in AZ, I use a combination of an HLN-200 water filter and a portable water softener. Otherwise, my dishwasher and clothes washer would have been quickly destroyed. I had to back flush and replenish with salt about every ten days. We don’t drink or cook with the softened water, so I ordered weekly delivery of Sparklets service. It was nice to have hot tea and chilled water on tap.

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