Just one more comment on use of FW for showers. I often camp in the desert SW when temps are relatively high and access to water can be limited. A daily shower is almost a necessity.
When I really want to extend my trip, there are some options. First is to give up on washing hair every day. A quick rinse without using soap works pretty well at least for a day or two and cuts down on the 1 gallon of FW I typically would use for a shower.
Next is a sponge bath to substitute for a shower. With proper technique you can do really well with less than a quart of water. You can even use "body wash" instead of regular soap. Just be sure to get an appropriate product. Typically they will be advertised as "hospital grade, no rinse" or some similar description.