To expand on the water tank thread...
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, it'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!
