It depends on how long I'm staying.
If I am in hot weather and planning to stay more than about a week, I will usually fill the fresh tank and add 1/4 cup of bleach. I'll then run off of the city water unless the water pressure drops to a point where it's difficult to use for showering.
The water pump will always give great pressure, and one quarter cup of bleach to roughly 70 gallons of water is unnoticeable, but it is nearly twice the amount needed to safely sanitize water for drinking, which would be 560 drops for 70 gallons. One quarter cup is 1,184 drops of bleach. Sanitizing drinking water is eight (8) drops of bleach per gallon of water.
At this higher ratio of bleach, it does prevent any growth that might otherwise occur in an empty water tank in hot weather. However, when running the water pump with this mixture, I will only use it to shower. I shut off the ice maker, and don’t run it into the line into the kitchen where we get drinking water. However, on the last day, while packing up, I do run the bleach solution through all water lines and just leave it in there. Then you water lines are nice and clean.
I have found the easiest way to get bleach into the fresh tank is to unscrew the water filter, take the filter out, put it in a sandwich bag, add one quarter cup of bleach to the water filter housing, screw it back on, then switch the valves to fill the fresh tank. Once the tank is filled, I take the water filter housing back off, replace the water filter and screw it back on.
When I know my rig is going to be parked for a month in southern Georgia in the summer, I add a full cup of bleach to the fresh tank, fill the tank and I then run that solution through all of the water lines and leave it in the lines.
Some people worry that bleach contaminates the environment. Bleach begins as salt water and ends as salt water. It does not contaminate ground water or anything else.
I keep a pan that holds two gallons of pure bleach in the attic of my home. The temperature gets will over 120 degrees in the summer, causing the bleach to slowly evaporate. It prevents any growth of mold. Once evaporated, you can see how it has crystalized - returned to salt.
Here is a chart to guide the about of bleach you can safely use in drinking water.
https://www.clorox.com/how-to/disinf...rifying-water/