Conserving water in an RV will take the worry out of running out of water when you are dry camping. Water conservation is important if you are far from a source of fresh water and want to stay camped in one place of more than a couple days. This is a double edged sword in your favor. If you save water and use less, you also slow down how quickly your gray and black tanks get full.
One way to save water is to wash dishes in plastic tubs in the sink. We measure and use exactly the same amount of water every time we wash dishes and rinse them. We are not full-timing yet, but we eat dinner in our motorhome every night. This is how our dishes are done daily..
If your gray tank fills before your black tank, pour the used dish water down the toilet instead of the sink. Better yet, save the dish water and use it to flush the toilet.
Navy showers are the normal advice for saving water. A Navy shower originated on ships with limited fresh water. It is simple. Turn on the shower water and get your body completely wet, then turn off the water. Soap yourself and wash without more water. When your are washed, turn the water back on and rinse yourself off. You only use enough water to get wet and then to rinse.
Here is another method. Heat a large pan of water on the stove. Only warm enough not to burn yourself. You can add some cold water to make it useable if you heat it too long. Bath using only that much water. More than a sponge bath, but less than a shower. It works.
If you were stand in a large plastic tub, you could save this water to flush your toilet. Remember, this is to extend the time you can stay dry camping out in the boondocks. For an extra day or two without heading to town for a dump station, drastic measures just may be worth it to you.
When washing your hands or face, use the small pump bottle of hand soap that puts out a lather of foam instead of a thick glob of hand cleaner. It is hard to use too much soap with these dispensers. We use one made by Dial soap. This soap rinses off of hands easier and will use less water.
Turn off your water pump except when you are actually running water. What this does it stop the toilet from using water when you flush only liquids. Why use a limited water supply to only get rid of water? I hope to put a momentary push button switch in my bathroom. It will disconnect the water pump only when the switch is pressed. This will allow me to flush liquids down the toilet without running fresh water along with the flush. You conserve fresh water with this technique and at the same time your black tank fills up slower.
If you want to clean the inside of the bowl, use a spray bottle with fresh water in it. Just spray as much as you feel is necessary and then flush. Again, flush with the water pump turned off. That spray bottle of fresh water is also handy to clean "skid marks" off of the bowl. An RV toilet does not hold and flush waste the same as a home toilet, so this tip helps keep the bowl cleaner.