I can tell you three things that will make a big difference ...
- How you manage showers. Obviously depending on how dirty one gets, can you manage to only do a "wash cloth" wipe down rather than take a shower? If you're only driving (not out hiking, etc) for the day, you really don't get that dirty. Even when you do take a shower, never let the water run. Rather, wet yourself down and then shut the water off. Soap and suds to clean yourself. Then turn the water back on only to do a quick rinse of the soap/shampoo. It takes some discipline but you'll save a huge amount of water. You'd be surprised how little you use if you just wet/wash/rinse rather than letting the water cascade over you constantly.
- Also, don't do dishes. Rather, buy paper plates/bowls and plastic cups and fork/spoon/knives and burn them (if you can) or throw them away. You save a massive amount of water no having to wash stuff. Yes - It's wasteful to throw away single use items. It's a trade off. Ecologically I don't know which is worse; wasting water, killing trees, or abusing the world with petrochemical release? But, the goal here is to conserve water, and if you don't have to wash any plates/cups/silverware/bowls/etc, you really conserve water. We used to wash all our stuff, and gave that up for the convenience of just burning/throwing stuff out. It's not really a vacation if my wife has to do 1/4 hour of dish washing by hand after every meal. The only stuff you have to really wash is the large pots/pans (if you use them at all). Our meals are simple and easily managed on paper/plastic. About the only thing we wash out is the reusable plastic wear (TupperWare, etc) because we intend to keep it.
- The other stuff like hand washing and brushing of teeth is easy to just not let the water run unless you are actively under the water. Many people have the habit of running the sink while in the act of brushing teeth or physically washing your hands, but the only time you NEED water is to rinse off the soaps. It's nearly identical conceptually to the shower concept. Don't run the water until you NEED it, not just because you're used to running it like being at home.
Those three things will conserve a huge amount of water no matter how large or small your tanks are.
Life's about choices!