A guide to various types of water filters and what you need to use where.

Choosing the Right Water Filter

Choosing the right water filter for your application can be a daunting task.  What are the differences between various types?  Does it really matter if I’ve got the right microns?

I’ve looked all over — in stores and on the internet — and never been able to find much in the way of a “which filter is right for me?” guide.  The longer we cruised, and used filters for various purposes, the more I had to learn about the topic.  The following summarizes what I know, but always check manufacturer documentation if using a filter as part of another system, such as a watermaker — I can give some general guidelines below, but your system may have specific requirements.

Water filters — called “cartridges” by manufacturers — have 3 basic differences from one to another:

  • Size. Obviously, you need the right size to fit your housing.  The standard size used in most housings is called 10″ by 2-1/2″ diameter.  Note that although it’s called 10″ long, the filters are actually about 9-3/4.”  While many other sizes are available, this is the size that I discuss in my article on water filtration systems and in this article.
  • Type. Six types of filters are commonly found:  pleated paper, string wound, polyspun, carbon wrapped/impregnated, granular carbon and carbon block.  More on these below — the various types do look different, which can help if they are labeled in a language that you’re not totally fluent in.
  • Micron rating. Filters all have a micron rating on the label.  The smaller the number, the finer the filtration.  I’ve seen them as large as 40 microns, but 20, 10 and 5 are far more common.  The smallest I’ve seen is 0.5 microns.  Finer filtration can slow down water flow, but that is usually more of a problem in houses (where people expect greater flow) than in boats.

You really don’t have a choice on the size, so I’ll look at the various types and the micron ratings.  Prices that I list are for buying online in the US or in big-box stores.  In other locations, prices can vary considerably!

One online source that has pretty good prices is DiscountFilters.com, which graciously allowed me to use their images of the various filter types.

Dirt and Sediment Filters

Image of pleated filter

Pleated filters. Pleated filters only filter dirt and sediment from the water.  They do nothing to improve taste or remove chlorine or microorganisms. They are fairly inexpensive, generally costing less than $5 each.

Pleated filters come in two varieties: pleated paper and pleated polyester.  The paper are generally the cheapest but can deteriorate quickly, while the polyester are far more bacteria- and chemical-resistant.

Pleated filters are most often used as a prefilter for the salt water intake on watermakers.  Most people don’t use them in drinking water systems.

Most watermaker companies recommend a 5 micron pleated polyester filter as a prefilter, but you should check the specs for your particular system.  Many cruisers try to rinse these and reuse them, with varying success.

Image of string wound filter

String wound. String wound filters look just like they sound — a bunch of string wound around.  As with the pleated filters, these are for dirt and sediment only and are used almost exclusively for watermaker prefilters.

Many of these now have dual filtration levels, with water passing first through a larger micron level to get the larger particles, then a smaller level.  The theory is that the filter will last longer before it gets plugged up.

String wound filters are relatively inexpensive, often under $5 but $7 or $8 for the dual-layer ones.  They cannot be rinsed and reused.

Image of polyspun filter

Polyspun filters. Polyspun filters are the third style of dirt and sediment filters.I’ve found several reviews stating that polyspun filters seem to last slightly longer than string wound, and may be slightly cheaper.  Again, they cannot be rinsed and reused.

Our Experience: We used all three of the above types for our watermaker prefilter, depending on what was available where we were.  Focus more on getting the correct micron rating for your application and don’t worry which of these types you’re getting.

All of them work well for dirt, sediment and rust; none will improve taste, remove chlorine or filter bacteria or other microorganisms.

Carbon Filters

Then we come to the three types of carbon filters:  carbon-wrapped/impregnated, granulated carbon and carbon block.  All three will improve taste and remove chlorine, but they do have important differences in how well they do it and what else they do.

These are generally used in drinking water systems and sometimes as part of a watermaker fresh water flush system (to remove chlorine if you use bleach in your water tanks).

Carbon wrapped filterCarbon wrapped or impregnated. These are generally the cheapest of the carbon filters.  They are also the type of carbon filter that is easiest to find.  If you are simply seeking to improve the taste of your water, most will work fine.

However, it’s important to note that they REDUCE the chlorine in the water, they do not totally eliminate it.  Do not use these in any application — such as the freshwater flush system of a watermaker — where total removal of chlorine is needed.  Any amount of chlorine will damage a watermaker membrane.

Generally, these are polyspun or, less often, pleated filters that have a covering of carbon.  Most often, they are offer filtration levels of 2 to 20 microns.  I’ve never seen one that is fine enough to remove bacteria or other microorganisms.  If you just want something that will remove most dirt and chlorine from your drinking water, these will work.  They typically cost just under $10.

Granulated charcoal filter

Granulated Charcoal. The big thing to know about granulated charcoal filters is that they do little to filter sediment from the water.  Further, they do not come in fine enough filtering to remove giardia.  They are easy to identify as they have a solid plastic outer casing.

Granulated charcoal filters are reasonably good at removing chlorine, volatile organic compunds, pesticides and many other man-made substances. They typically come in 2 to 20 micron filtration levels.

The best use for granulated charcoal filters is simply to remove bad taste from drinking water.  Like the charcoal wrapped filters, they do not sufficiently remove chlorine to use on a freshwater flush system with a watermaker if you use bleach in your tanks (or if you alternate watermaker water with city water that could contain chlorine).

Granulated carbon filter typically cost $10 to $12.

Carbon block filter

Carbon block filters. The most all-encompassing filters are carbon block filters, but that doesn’t mean that just any carbon block filter will do.

Only the finest 0.5 micron carbon block filters will remove giardia and cryptosporidium, both of which can cause severe diarrhea.  The 0.5 micron carbon block filter is also virtually 100% effective in removing chlorine, and is what most watermaker manufacturers recommend on their freshwater flush systems to ensure that no chlorine reaches the membrane.

Our boat came with a Seagull filter for our drinking and cooking water, and they use a proprietary filter cartridge.  However, if we’d had to install a filter ourselves, the 0.5 micron carbon block filter is what we would have used for our drinking water.

A carbon block filter’s effectiveness at removing sediment is dependent upon the micron rating of the filter, although water with visible dirt and sediment will quickly foul the highest quality carbon block filters.  Carbon block filters can remove small quantities of heavy metals, but they can’t cope with high concentrations and shouldn’t be relied upon for that.

Carbon block filters can be made from any of several materials; coconut shell carbon is the best, but also costs a little more.  A 0.5 micron carbon block filter will cost $18 to $20 (some brands more).

While sediment-only filters can simply be changed when the flow rate has noticeably lessened, carbon filters will lose their full effectiveness long before taste is affected.  If you are using a very fine carbon block filter, be sure to change it according to the manufacturer’s directions in order to get the full benefit.

One final note:  we could never be certain of finding the really good carbon block filters in Mexico and Central America, and would buy them on trips back to the US and take them back in our luggage.  Since I could never be certain of finding them in local stores, so I simply resorted to buying them online.    Try DiscountFilters.com.

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  • galen
    Posted at 11 April 2011 Reply

    I use a .1 micron on my house with a 20″ filter. I was surprised at the high flow rate. I precede this with a sediment filter and after it with an iron reduction filter. I live in the swamps of the Chesapeake Bay.

  • Richard Edwards on Facebook
    Posted at 13 August 2012 Reply

    Thank you for the info, learned something new.

  • Randy Price on Facebook
    Posted at 11 April 2013 Reply

    Great read. We use a 4 stage system after a standard strainer – 5 micron, 1 micron, solid block carbon, followed and polished off by a UV light. Hasn’t let us down yet.

    • Gene Magee
      Posted at 19 July 2016 Reply

      Hey Randy! Many years later, but what UV system do you use?

  • RB
    Posted at 03 May 2013 Reply

    Thank you for this very informative post. I found it very helpful in selecting which filters to purchase. Ryan, East Hawaii

  • John Ahern
    Posted at 19 December 2013 Reply

    How long on average does a filter last?

    • The Boat Galley
      Posted at 19 December 2013 Reply

      It really depends on the size (microns), the water quality, and how much water you put through it. Putting a large volume of somewhat dirty water through a very fine filter will cause it to plug up much more quickly than half as much clean water going through a coarse filter. Typically, they’d last about 3 months for us . . . but whenever we were heading to out of the way places, we’d assume they’d only last a month and stock up. The non-charcoal filters will slowly allow less and less water through, and you can simply change them when it gets unacceptably low. The charcoal filters will usually be labeled with how often to change them.

      • Stu Meisner
        Posted at 30 May 2014 Reply

        Can a hand pump such as a small fynspray be used with a system with fine filters one could buy at a plumbing supply. In your initial article you said that these plumbing supply systems could be used with a foot pump, but does that include both a hand pump and fine filters ?

        • Carolyn Shearlock
          Posted at 30 May 2014 Reply

          I haven’t personally tried it. A lot will depend on how much “suck” the pump can develop — a foot pump is pushing the water through the filter, which is much more efficient than a hand pump, which by its very nature, is right at the outlet and hence trying to suck the water through the filter. I’d check with the manufacturer of the hand pump if it’s critical.

  • June Ruby
    Posted at 19 December 2013 Reply

    Thanks, Carolyn! Do you have an article on watermakers? I would like to know how we should be testing our water, what ppm is typical and acceptable, and how to tell if the membrane is still good.

    • Carolyn Shearlock
      Posted at 19 December 2013 Reply

      Hi June! That’s one topic that I haven’t written about, partially because there is such variety between systems. Most systems have some way to divert a bit of product water into a glass and then you can use a tester like this one (this is the one we had and many other boats did too, costs under $20) — there’s a sticker on the back of it to tell you what acceptable tds (total dissolved solids) levels are.

      Membranes will fail in one of two ways — either plug up so that the output just gets lower and lower, or be “destroyed” so that it’s not doing as good a job and the tds level will get higher and higher until it’s unacceptable.

  • Blue96bird
    Posted at 25 May 2014 Reply

    Thanks for the info!! You’re right. This is about the only site with a good write-up.

  • Ivan
    Posted at 23 June 2014 Reply

    which carbon block filter from discount filters would you recommend? (general drinking cooking use)

    • Carolyn Shearlock
      Posted at 24 June 2014 Reply

      I like the extra protection that the 0.5 micron filters give. Assuming you have a standard 10″ housing, this is the one I’d go with (be sure to check the specs to make sure it’ll work for you, I’m making assumptions about your system):

      • Ivan
        Posted at 24 June 2014 Reply

        Ok thanks I ordered that filter, now I’m looking at standard housings… Many to pick from… Do you know of any solid rated models?

        • Carolyn Shearlock
          Posted at 28 June 2014 Reply

          I don’t really know that any are particularly better or worse than others. A handy feature to have is a pressure release button — makes it easier to unscrew the bottom when you need to change the filter. Also, get one that uses standard plumbing parts to connect to your water hoses, not any special proprietary quick connects (if one fails, it can be hard to find a replacement).

          Read more in my article about Water Filtration Systems:

  • Lupari Sue
    Posted at 04 July 2015 Reply

    And then there is ceramic..works like carbon filter…similar microns effective against Giardia anc cryptosporidium. and can be scrubbed ( we use a Scotchbrite scrubber) and doesn’t need to be replaced. We use ours after a sediment filter. Everything goes through sediment filter and use the ceramic filter just for drinking water.

  • Patti Holma
    Posted at 04 July 2015 Reply

    Practical Sailor has a 3 part series starting with June issue on various aspects of clean water

  • Macster
    Posted at 01 November 2015 Reply

    I have been using polyspun filters for a while.. I have noticed that if I spray them with a hose, the layer of rust comes off real easy and the filters ends up pretty clean.. my questions is, even if it looks clean and reusable, I shouldn’t re-use it?

    • Carolyn Shearlock
      Posted at 02 November 2015 Reply

      Some people do re-use them after back flushing and spraying. If you’re just using them to remove sediment, it should be okay to reuse them if the flow is okay.

  • Karen
    Posted at 18 January 2016 Reply

    I have been using a smaller pitcher PUR system, making water and transferring to larger containers (one for the dogs and one for our drinking) so we have a supply to keep on hand. It was working great until we got unto warmer weather and I noticed the 2 containers started growing green algae. I washed both containers and changed the filter, but it continues to be a problem. Any help would be appreciated.

    • Carolyn Shearlock
      Posted at 18 January 2016 Reply

      Storing water for any length of time — particularly in clear containers — will let algae grow. The best way to stop it is bleach . . . but that’s one of the things we’re trying to filter out. Instead of filtering into containers, we just filter (with the dispenser) as we need it.

  • Anne
    Posted at 12 June 2016 Reply

    Helow,, thankz for your write up,, I’ve learned a lot,, anyway I have a water station and my problem is the taste… How can I improve the taste of my product??,, please help ne thankz

  • Victor
    Posted at 05 July 2016 Reply

    Good article Carolyn. We have just purchased a ceramic filter for drinking water and will let you know how we like it. As a previous commenter said, the fact that you can scrub it with a green pad when it clogs has a great advantage. Of course we have a spare just in case.

  • Tory Salvia
    Posted at 06 July 2016 Reply

    Excellent article on water filters. I’ve shared it though Facebook with our viewers and emailed it to a shipmate with a water-maker.

  • Flash wheeler
    Posted at 15 July 2016 Reply

    Best article I have seen. THANK YOU !

  • Colette
    Posted at 21 September 2016 Reply

    I don’t have a boat, but needed to know which type cartridge to use for my home and our VFW Canteen. No one else breaks down the types and their strengths and weaknesses. Thank you so much for posting this. Our sandy soil and wells require the pleated. 🙂

  • Rambabu D
    Posted at 03 July 2017 Reply

    In my home town.. water color is greenish and we placed the sand filter + activated carbon filter + 5 microns Yan filter.. still water looks greenish. So any one can suggest which filter can reduce the greenish color in water

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