Join Date: Nov 2008
Location: Deale, MD
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Best filtration for freshwater: just particles, or carbon too
The conventional wisdom is that leaving the chlorine in is positive, because it provides residual disinfection. However, for the typical user that adds water perhaps less than once per month, there isn't any residual after 2 days and the argument may be faulty if there is any dirt harboring growth that the chlorine did not reach. Additionally, the residual chlorine did nothing for the plumbing if the water was filled upon returning to the dock. Also, if the tanks was only topped-off 20-40%, the residual chlorine is almost certainly too little to provide consistent benefit.
At some marinas (mine) the water is from a well and is non-chlorinated. The residual factor is mute and I have always used a carbon/particle combination on the end of the hose (it is removed from the hose between uses). I rinse the boat a bit first to clear the hose.
Another point of view is that carbon will remove substantial TOC and other reducing agents that are required for bacterial growth. Yes, many bacteria can use CO2 as a source of carbon, but only if there is an alternate electron donor available, and carbon should remove many of these also. Given the water tank should be in complete darkness, we should be able to rule out algae.
Occasionally we hear of a tank gone sulfury; likely the bacteria are using sulfate along with organic material. Related to the question. That more tanks do not go sulfury (all water has sulfate) suggests
Any filter media can harbor growth, though KDF media is said to retard this.
A third option is to filter with carbon and then to add chlorine back. The carbon filtered water may have a lower chlorine demand. And extra step, of course.
And, of course, point of use filtration is a whole nuther' topic and I'm leaving it alone for now.
In the case of well water, more filtration is better, since the source is unsupervised. In the case of city water, I'm sure much depends on the municipality and even the infrastructure at the marina; is the hose reasonably clean?
Has anyone ever made a study of this? Too many variables, but I though I would ask.
(when asked how he reached the starting holds on a difficult rock climbing problem that clearly favored taller climbers - he was perhaps 5'5")
"Well, I just climb up to them."
by Joe Brown, English rock climber
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