If you stored your RV with antifreeze, you'll want to flush this completely. The antifreeze recommended for RV water systems is entirely different than the antifreeze you put in your vehicle's radiator. Please note that the antifreeze used in your vehicle radiator is deadly to humans and animals, and should never be used in your RV water system.
Flushing Your RV Water System
This isn't as complicated as it sounds. Simply hook your clean water hose to your garden tap, or city water tap if you are at a campground. Connect the other end to your RV clean water intake connection. Open your gray tank and turn on all the faucets. Flush until the water runs and tastes clean. If you don't have your gray tank hooked to a sewer, you might want to either catch the outflow in buckets or direct it to a proper sewage/gutter/drainage outlet.
Do the same with your holding tank. Turn the pump on and run several tank-fulls of water through it to flush any antifreeze completely out of the tank and pipes.
If you have any residual antifreeze taste you can flush your system by adding a box of baking soda divided up between the various drains. Either sprinkle it directly and run some water or dissolve it and pour it down the drains. Let it sit for a couple hours.
Disinfecting Your Water Systems
If you didn't store your RV with antifreeze--many people living in the Southwest, on the West Coast, and in the South probably didn't bother with this--you may still need to clean your system. Mildews and molds can be deadly, especially some strains of black mold. Make sure you disinfect your entire water system.
You can do this by adding one cup of liquid bleach for each 20-30 gallons of water. Flush this through your system and let it sit for a couple hours, but no more. Chlorine bleach can disintegrate synthetic seals if left for too long. Chlorine bleach is also highly effective in killing bacteria, molds, mildew, and viruses, so you can rest assured your system will be as clean as the water you run through it.
Flush this thoroughly, then to help get rid of the chlorine taste, flush with the sodium bircarbonate (baking soda) solution.
Most people like to flush their water before they leave for a trip, just so they can enjoy their time away without having to do these chores.
Keeping Your Water Fresh
Many RVers have added water filters to their RV water system. During trips, you're safe to add a couple tablespoons of bleach to your holding tank water to keep it clean and drinkable. Alternative water purification solutions (powders or liquids) are also available through camping departments or online outlets.
If you're boondocking you'll want to make sure you can keep your water fresh for several days, especially where it's hot. Water in dark spaces is the perfect environment for growing bacteria and mildew. If your water tastes funny, don't drink it.
Drain your system completely when you return from your trip, and plan on repeating these steps after leaving your RV unused for more than a few days. Stale water rapidly becomes undrinkable water no matter how little there is. Dampness is all it takes.
As a final resort, make sure you have plenty of drinking water with you when you're traveling, Rving or camping. Anyone can break down at anytime. Flat tires happen. We've had the water shut off in different RV parks due to different reasons.
Once the well went dry, and though our drinking water was sourced from a separate piping system, they had to shut off all the water while they drilled a new well. Fortunately, this lasted only a few hours each of two days, but having bottled water on hand made the difference as the park owner neglected to tell any of us that we'd be without water for that time. Just glad I hadn't gotten all soaped up in the shower when the water went off.
If you're near a flooded area, you might find that you're water sources are affected by the needs or damages of that area. If you're in an area that is suddenly affected by any disaster, you might find supplies of bottled water become a scarce as fresh water.