Dear HJL,
The referenced article [1] was pretty complete and detailed; I just want to add a couple of details. First, when I fill my storage tank with the intent of leaving it unattended and unused for a long period of time, I usually dose the water to about 7 PPM Chlorine. Then I check it every time I visit my distant retreat, supplementing the chlorine dose if the reading gets to 2 PPM or less. Levels at and above 7 PPM are dangerous to your health but draining the right amount of water and adding untreated water to the tank will bring it right down to the correct and safe drinking level of less than 3 PPM.
The thing that we want to know is the residual-free chlorine still available to treat what is in the water that should be treated or might come into the system. To do this I use test strips that will tell the residual chlorine concentration between 0 and 13 PPM. These strip show a distinct color for each distinct concentration, making them much easier to read than pool test kits.
I want to disagree with the placement of the tank directly on the concrete floor for a couple of very reasons. First, a tank, that has the ability to provide water through a period of three or four weeks when you can not refill it, can not be easily manhandled. At two gallons/per person/per day, a 100-gallon tank will cover 50 man days or less than a month for two people. Add two children and the time is 12 to 13 days. I designed my system for 60 days survival without replenishment because water is survival!
Secondly, in most situations adequate sized storage tanks are too heavy but to install except on a slab, basement floor and almost certainly will require manually filling containers and manually transporting those filled containers. I selected the square, stackable, 5-gallon water jugs sold at many prepper-oriented web sites. My 1550-gallon tank sits on a well-engineered (my wife says way over-done) platform that is just high enough that I can sit two of those five-gallon jugs on the floor and let gravity fill them until the tank bottom is nearly dry. My well system is pumped in to a very large captive air tank with the pressure switch set at 35 psi; from there the well water is plumbed in 1″ PVC to a booster pump that serves the house and a branch that directly leads to the 4″ ball valve at the tank via a tee that serves the tote filling piping on the other side. The totes used are similar to PN 400 with a M110 valve that is removed for filling. None of this will be very helpful if the means of refilling the storage tank are forgotten. I have two generators, each capable of running the well pump. I would replenish my storage tank at least once a week in a grid down situation, until my fuel storage was depleted. – B..J.