Saturday, June 3, 2023


What kind of water filter do you really need?

By Greg Illes

We shower with it, flush the toilet, wash dishes, and (most importantly) we drink it. Behind the scenes, it also runs through all of our expensive, hard-to-service plumbing and fixtures. It hardly needs to be said that we want good, clean water in our tanks and pipes.

For most folks hooked up to an RV park’s water system, good water is simply a fact of life (although there are some noteworthy exceptions, usually associated with well water or old plumbing). But even if you are using “city water” direct, or to fill your fresh water tank, there are some good reasons to use a water filter, and the right kind, all the time.

1. Something you can see: Even the purest water will accumulate sediment, especially when it’s run through older piping systems. This fine-to-coarse material will crud up your valves and build up in your fresh water and water heater tanks.
2. Taste and smell: Chemicals in the water can make it stinky and nearly unpalatable.
3. Bugs: Parasites come in all shapes and sizes. Fortunately, typical certified water systems treat their products with chlorine, and most bugs are killed — but not all.
4. Invisible stuff: Some toxins and pollutants cannot be seen, tasted or smelled, but can wreak havoc with your health nonetheless. Again, properly treated water systems are rarely victims of such contamination.

So are you using “hook-up” water most of the time or do you occasionally draw from an untreated source? Your filter requirements will vary greatly depending on the answer. For the sake of this (short) discussion, let’s ignore “swamp water” users and focus on the vast majority of us “city water” consumers.

When you’re traveling about in your RV, you really can’t know what the next water-quality issue might be. So filtering for No. 1, No. 2 and maybe No. 3 are of the greatest interest.

For No. 1, a sediment filter is the type of choice. But these come in a bewildering array of “sizes,” meaning the filtration pore size. A typical cheapo in-line filter will have a pore size of about 100 um (micron), or roughly the diameter of a human hair. This is enough to keep out the sand, but not the silt. With this filter, the coarse dirt will be refused, but you could still see a fine brown film (rust) on your precious plumbing. Finer pore sizes are better, but will have slower flow. By the time you get down to about 0.5 um, the filter will keep out not only sediment but also the common biohazards like Giardia and Cryptosporidium cysts (which are not killed by chlorine). But at 0.5 um, water flow will slow significantly and you may need a larger filter (or two in parallel). A 5 um filter is a happy medium if you aren’t worried about cysts.

For No. 2, activated carbon is the choice, removing taste and smell and delivering great drinking water. Fortunately, many filter products are available that combine sediment and charcoal filtration in one cartridge; you just have to be meticulous about specifications so that you know what you’re buying and what it can do. In order to get exactly what you want, you will likely have to buy a housing and filter cartridge separately. These are widely available. I like the clear housings so I can watch for sediment buildup (see photo).

For a full-flow input filter you can use a 5 um type for good flow, and then deploy a 0.5 um filter for just your drinking water, which doesn’t need so much flow as filling a tank or running a shower. Extra trouble and expense, but what is healthy water worth to you?

There are some exotic filtration technologies available such as UV light and others. Please bear in mind that this short article cannot cover a lot of the detail in water filtration techniques and their advantages and/or disadvantages. Entire books have been written on the topic and extra reading is advised if you want to be well informed (and protected).

For reference only (your needs may vary), the products I use are shown in the photo:
Pentek 15071 housing (takes standard 10-inch filters)
Pentek EP-10 filter (5 um sediment + charcoal)
I also added quick-connect hose fittings for easy use. All are available on Amazon: water filters and hose fittings.

photo: Greg Illes

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 blog at


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