Chlorine Removal with Carbon Filter


Hi Mark,
Your comment about having a carbon filter reminded me of something. Like you, I have a 10" carbon filter to prevent chlorine from damaging the desalination membranes. We also use one when filling our tank with (verified) dock water. I noticed on a sticker that it was rated at 2 gpm. I did some research to discover that these are rated at 1, 2, or 3 gpm depending on what a manufacturer claims. More Googlerian research revealed that chlorine removal is dependent on the length of time water is exposed to the carbon as it flows through. These are not high rates

Anyway, it seems that when filling your tank or flushing the water maker that slower is better....1 gpm is slow. When we have the luxury of time we use this rate to fill out tanks.

We think it is very difficult to control the flush rate by cracking the, 3 way. When flushing our membranes I turn off our water pump and let the accumulator tank run out of pressure. Then I open the flushing valve fully and control flow by short pushes on the water pump breaker. I keep water flowing for the 3 minutes of recommended flush time. You can monitor the flow pressure on your Dessalator panel.

BTW Seagull filters are also rated at just over 1 gpm based on the same constraint. They even sell kits for restricting the gpm to 1.

Bob, KAIMI SM 427

Alan Leslie

We use a combination 5u/ carbon filter in the filter housing when in a marina...but try NEVER to put marina water in the water tank.
At sea we use just a standard 5u filter.
We have a fresh water valve and also a sea water valve from the sea chest...never had any problem with these Italian ball valves..
Elyse SM437 


One of the things you find is that different watermaker manufacturers have different worries about what will impact the membranes.  Strange, because they are all using the same FilmTec membranes.  Just as an example, Spectra (for example) worries a lot about biological fouling, and is rather blasé about chorine.  Dessalator is exactly the other way around.

A good industrial carbon block filter (probably not one you get at Home Depot!), used at its rated flow rate typically is specified at 90% removal of free Chlorine in one pass.  When I fill my tanks from the tap, I filter it through a carbon filter.  When the water goes comes out of the fresh water pumps, it runs through another filter.  The branch line that goes to the water maker has ANOTHER carbon filter in it. If you are counting, that's (theoretically) 99.9% removal of chlorine. I do not worry about chlorine getting into my membranes.

When I bought the boat the previous owner had the "no tap water in the tank" rule.  They had added a pressure reducer and plumbed a shore water fitting into the pressure side of the water system so they could use dock water without adding it to the tanks.  I never use this connection.  

I have seen three boats sink at the dock because of broken freshwater hoses.  To take a boat with watertight bulkheads and very limited underwater through-hulls and then attach an infinite supply of water into the hull just seems the very antithesis of the Amel design philosophy. On those relatively rare times these days when we need to take on dock water I fill the tank when needed--then turn off the dock water and put the hose away until the next time.  

Bill Kinney
SM160 Harmonie
Culebra, P.R

Mark Pitt

This discussion of an extra carbon filter between the fresh water pump and the water maker flush reminds me of an incident on my SM last summer.  On an overnight cruise, my wife noticed the bilge pump was on when she went to the head and was also on when she returned.  She checked the bilge pump counter (Aqualarm Bilge Pump Cycle Counter, thanks for the recommendation Eric!) and it revealed there had been many bilge cycles.  I looked in the engine room and found that the 10 inch filter cartridge housing had split and fresh water was gushing out.  This was not the Amel/Dessalator housing supplied with the watermaker but one that I had added.  I lost one-half a tank of fresh water.  

The housing was about 6 years old and either had a defective weakness since manufacture, or the heat of the engine room caused it to weaken.  I am replacing it with a Pentek 158319 1/2" #10 High Temperature Slim Line Black Housing that is rated for 160 degrees Fahrenheit.  Standard housings are made from styrene-acrylonitrile (SAN) and are rated for 125 degrees.  That gets close to engine room temperatures when the ambient temperature is high.

Mark Pitt
Sabbatical III, SM#419, Carloforte, Italy