I always find discussions of poteable water interesting, but also see a lot of mis-information included in them. So, I'll jump in here with my 2 cents worth as a four year liveaboard, a 30+ year weekend warrior and a research chemist who spent 10 years trying to understand the effect of poteable water on plastic plumbing.
The water we drink is way more complicated than the chemical symbol H2O suggests. Because it is the closest thing we have to a universal solvent, pure H2O doesn't exist outside of carefully prepared lab specimens. The water we drink has many chemicals and microbes in it. Most are good for us (minerals) and some of the microbes are not.
Preparing water for distribution to our homes is a science of its own, and unfortunately not always well understood by the smaller water companies in the smaller cities of the US. However, they all need to meet well established criteria for drinking water; toxic chemicals, carcinogens and microbes must be kept to a minimum. Unfortunately, our standards do not include maximum levels for chlorine as they do in Europe. Most of Europe used to set 0.1 ppm chlorine as a maximum where here that is pretty much the minimum you find. So we find residual free chlorine levels vary from 0.05ppm to nearly 10ppm. You don't want to drink the latter. A microbiologist once told me 10ppm chlorine in water will kill a horse. But that level is rare, and you can smell it if you sniff test a glass half full.
I mentioned carcinogens. When source water contains certain organic materials such as the flora and fauna in surface water (lakes & rivers), carcinogens called trihalomethanes (THM's) can form when chlorine is added to disinfect the water. To avoid this, disinfection is accomplished with alternative methods most commonly using 'combined' chlorine in the US. If you have something growing in your water system, you will likely generate some THM's if you add chlorine.
In spite of all this, municipal water is almost invariably safe and has enough residual disinfectant to remain so in modest storage so long as you don't run it through a charcoal filter which absorbs the chlorine residual. Bottled water however has no uniform standard. Studies have shown that bottled water can be risky and is frequently or maybe even usually less 'safe' than municipal water. Consider the stuff you get from the local RO system at the supermarket. Does it get tested for quality? When? By who? How about that bottle that you might refill?
So my point is the city water you bring on the boat is likely to be better for you than the bottled water providing you maintain your water system correctly. This includes the delivery hose. We have been drinking the tank water on our boats since at least 1979 and have never had a problem. I can't remember having shocked the system more than a few times in those years only to find out I didn't need to.
What we do is simple starting with a suitable, clean hose.. First, never take on water from a marina that uses a well, unless there is no alternative. Always look for city water. If you must take on well water, then and only then would I consider adding some chlorine, say 0.1ppm. Otherwise, put clean water in a clean system and use it for everything. On Chateau de Mer we carry 180 gallons and that can carry us two weeks if we are cruising and being frugal, less if we are at a dock and enjoying a water source.
The alternative of using dockside pressure water has several downsides. The water in your tank will get stagnant and you won't want to drink it if you go off for a cruise, the delivery hose that sits in the sun all day will produce green water that will get into your system, and if you are as forgetful as I can be, you might go off and forget to turn off the water.
What about filters? Well, if you are using tank water regularly, you probably don't need one. There is not a lot of sediment that gets into city water. The 'taste and odor' filters that have some charcoal in them can be beneficial, and I use them in certain circumstances, BUT they also have a downside. The charcoal that is supposed to remove odors also removes the residual chlorine that you want for disinfectant. When this happens, the very high surface area of the charcoal that does the absorbing also provides an excellent medium for growing bacteria! That is the slime and foul odor you get when you pull one out. And also have a look at the cannister. It will likely be dark or black on the inside. If you must have a charcoal filter and want to minimize the smell from growing bacteria, you can try the 'silverated' filters. These have a fine coating of silver on the charcoal which which acts a biocide. They do retard the growth of bacterial slime a bit, but are not worth the added cost IMHO.
Here in south Florida where the water is high in sulfur, I find the smell generated by the filter builds up too fast; so I don't use it here. When north, we leave it in because it is plumbed already.
Now on to adding chlorine for shocking or maintenance. The city of Miami shocks its water system each year just before the snow birds arrive and start to increase the water usage. The water district told me they use about 10ppm chlorine to do this and that is enough to drive out all the bacterial crud that forms over the summer. And 10ppm ought to be the maximum you use for shocking your system if it really needs it (first make sure the filter is not the cause of the unpleasant taste and odor). But keep it to a minimum. Remember there are a lot of organic components in a boat water system that will be degraded by chlorine, even miniscule amounts. It's progressive.
For maintenance, once you have a clean system that you are using regularly, you do not need to add extra chlorine. Most all of us can trust our municipal supply. If for some reason you want to add chlorine, keep it to 0.1ppm.
My $.02.
Bob
PS, when we used to have to winterize, I found the best approach was to drain all the water out, use a wet vac to suck as much of the water as I could remove, and just leave the taps open. In the spring, I'd purge the first tankful and begin to use the water. No residual taste from antifreeze. Now if you were using vodka....
