If you plan on drinking the water in the fresh water tank, then you need to sanitize the fresh water system before using it. Do a search on Sanitize in the forums, and you'll get plenty of pros and cons to drinking the water you carry. Many of us do without any worries or problems at all.
To sanitize, mix 1/4 cup of bleach for every 10 gals of tank capacity in a bucket with some fresh water, and carefully pour it into an empty fresh water tank. A funnel works well for this. Add water to fill the tank, and then pump the bleach mixture through ALL the fresh water plumbing, including the hot water heater. Pump until you smell the bleach mixture at each and every faucet, both hot and cold. And the toilet. Turn off the pump, and top off the fresh water tank. Let it sit for 4 hours at least. Overnight works quite well. Drain everything, including the hot water heater. Now, add 1 quart of white vinegar for each 10 gals of capacity to the fresh water tank. Fill with water, and then pump the vinegar mixture throughout the system, again until you smell the vinegar at each faucet, both hot and cold. Don’t for the toilet during all of this – you want the cold water pipe to it sanitized as well. Note – you really can’t add too much white vinegar, so more is better than too little in this case. Let it sit overnight, or for a couple of days. It will get rid of the bleach taste and smell. Drain everything again, and fill with clean fresh water. Then you can safely drink it.
Kay and I have been doing this for years upon years, and we have never gotten sick from drinking the water in the trailer.