Waterbed Care and Maintenance.

All Safety Liners have a tendency to move or creep down the side of the frame and in some cases pull the side of the foam frame down. This happens by sitting plum on the edge of the frame. It is best practice to avoid this by sitting over the edge of the frame when getting into bed and swinging your legs over.  Same when getting out. Sit near the edge with your feet on the floor and push up with your hands.

Safety Liners are there to catch water in the rare circumstance that your waterbed should ever develop a leak.
Check it from time to time to ensure it is as it should be. Push the bladder away from the foam frame where you hop in and out and if there are any creases in the liner, Pull it back up.  It is better to have a chair to sit on.

Various types of liners have been made to attempt to counter this liner creep. Bag liners that encase the whole foam frame.
I have seen many busted bag liners. And have seen many foam frames that look to have collapsed on the edge due to a bag liner pulling the side down due to trapped creases. Also, liners made from mattress material have a tendency to pull the foam frame down and sometimes the bladder at the edge of the foam frame gets trapped and looks to roll off early dipping at the side of the frame. Though they are much more durable. 

Perspiration can build up between the bladder and the top cover. In some cases, mold spots can appear on the bottom of the wool top. It is good practice in any bed to fold the covers back after arising to allow airing. Some beds with foam pillow tops can appear to be quite wet under there.
Leave the covers folded back whilst you prepare for the day.

Over time water evaporates and air bubbles form in the bladder, which if left untreated degrades the comfort of Your Waterbed. The air can make the bed sound noisy or sloshy. Worst case with excessive air in it. It can have the feeling of a loss of support due to the air moving about in it and you think that it needs to be topped up.  Best Practice is to burp or remove the air from it around every 6 months to ensure it is performing at its best for You.

Every so often your bed will need a small top-up. Maybe only a bucket or two of water once a year.  

Waterbed Conditioner. This keeps the water from stagnating and smelling bad. Conditioner also keeps the inside of the waterbed mattress supple, as vinyl can become brittle over time. Unless you are moving your water mattress, there is no need to change the water. Yet, you will need to continue to add waterbed conditioner once every year. And use vinyl cleaner on the bladder and liner to remove body oils.