I spent the bulk of my working career as a Master Plumber, I received
certification for Water Quality Ass'n training in water treatment, so
I've seen my share of ugly water. Still, I find it unusual and a bit
amusing that most folks will drink water from a tap without giving it a
second thought - it comes out of a spigot, it's OK. BUT.... Same water
goes to the hose bibb on the dock, and into a tank on their boat, and
suddenly, it's contaminated with everything from plague to festering
bacteria. Or just funky!
I've seen posts where folks describe pouring *gallons* of Clorox into
their tanks to sterilize them; some boaters refuse to drink the water
from their tanks for fear of contracting some dread bacterial infection
so instead, schlepp gallons of water in 12 oz bottles aboard and deal
with the storage and trash in order to be "safe". There is a lot of
misconception regarding water on board, and there's plenty of
misinformation out there that helps fuel the fire (and sell product!)
You absolutely can get sick from ingesting contaminated water, girardia,
coliform; those and a host of other bacterial & viral agents can be
present in water, and they *can* make you ill. The good news is, they're
relatively fragile, and rudimentary measures are proven effective at
eliminating potential contamination. Additionally, the bulk of the water
available to us comes from municipal water supplies; they are required
by Fed & State law to provide water that meets standards of potability,
and there are very few water suppliers who do not maintain rigorous
procedures to insure those standards are met. Water quality is the first
line of defense in maintaining public health, and those involved in that
endeavor take pride in their part of that process. We take for granted
that the water delivered to our tap is of good quality, and that's a
relatively safe assumption. Stories of sickness as a result of
contaminated public water supplies are almost nonexistent. With that in
mind, we can safely presume that public water we tank is pathogen-free.
(Oh, yes, I saw the story about brain-eating amoeba in a fire hydrant,
so dogs pee on them too. You drink from a fire hydrant? Click bait!)
Water that starts off clean doesn't spontaneously "go bad" nor can it
mysteriously become infested with bacteria- without a source for that
contamination. For all intents, clean water put into a clean tank and a
clean system will stay that way. Indefinitely. There's no real need to
continue to disinfect water that's already disinfected, although public
water contains an amount of "free chlorine" that is available to
disinfect additional contamination that may be encountered beyond the
initial disinfection. So given those parameters, we really need only to
insure that our on board system is clean. To do that, we can perform an
initial disinfection. Initial is key, provided we accept the premise
that clean water stays clean.
To disinfect a system, a basic rule of thumb to shock disinfect with
chlorine indicates we need to bring the chlorine concentration to about
50 ppm. Clorox contains 5.25% chlorine, so do a bit of math.
For a 100 gallon tank, multiply 100gal. x 50 ppm -> 100 X (50/1,000,000)
= .005 gal.
So we need to add .005 gal of chlorine.
Household bleach (Clorox) is typically 5.25% chlorine, so 1 gallon of
Clorox = 0.0525 gallon of chlorine.
For our 100 gallon system, .005gal/0.0525= 0.09524 gallons of bleach.
That converts to ~ 12 oz. So, 1-1/2 cup of Clorox is needed to create a
concentration of 50 ppm in 100 gal.
Contact time for a 50 ppm concentration is 6 hrs. For 24 hrs. contact
time, the concentration can be reduced to 10 ppm, or for 100 gal. tank,
a dose of 4 oz. Clorox.
These are conservative concentrations, meaning they're already
overkill. More isn't necessarily better - enough is enough! Higher
concentrations won't make the bugs more dead, they'll only complicate
the flushing and rinsing of the system. Once the tank is disinfected, it
should be flushed & rinsed with clean water, then it's ready to use. A
carbon taste & odor filter installed in the main supply line downstream
of the pump will remove any remaining chlorine taste, and help with
keeping the water fresh tasting and enable you to dispense with the
plastic bottles. Once the tank is disinfected, there's no need to
routinely disinfect it other than perhaps an annual preventive shock.
So *keeping* tanks suitable for domestic use simply involves filling
them with clean water and using it!
Hope that helps! Drink tank water! <G>
