I think part of using less water is meal planning.
I like to cook most meals (for shorter trips) before the trip, freeze, and just reheat in camp.
For example, I'll make and wrap burritos in foil (or not at all if I expect to have a grill) and freeze them and then just put them in the coals of the fire (or on the mainfold, depending on travel time). Or, for another example, I'll cook spaghetti and put it in a freezer bag or other liquid-tight container, freeze it, and then put the container in a small pot of water to re-heat. The water can then be used for beverages or washing, depending on needs, and if I'm solo, all I dirty is a fork and the container. If the container is a freezer bag, I'll re-use it to seal up the dirtier trash. If not, it's washed as below.
For long trips, I like to eat all day in the form of snacks. I'll have a breakfast of oatmeal (in my mug used for coffee/cocoa, without cleaning, rinse with water that I drink), some fruit, maybe a bagel, and a hardboiled egg or some similar protein. By 9:00 or 10:00, I'll have a large snack, usually trail mix, a piece of fruit, and some jerky. Have a sandwich or two for lunch (knife needs cleaning, but not with water), another snack mid afternoon, and a light meal for dinner. Very little that requires water to wash, and the dinner meal will be as above for the first few days (I only have a cooler) and then something that needs cooking for the last part of the trip.
Hot water does clean better because the higher temperature lowers the surface tension of the water, which makes it a better solvent. That's the same thing soaps/detergents do. When I'm solo, I don't use soaps at all to wash, just water that's almost too hot to put my hand into--no need for rinsing but scraping before washing is essential. My wife likes soap.
If I'm in the desert, I'll use the sand method, but tend to stay away from using organic materials: I don't know what kinds of molds or other microcritters are living on it. I do not use the sand method on beaches, especially near civilization. I know that there is still the possibility of finding microbes in the desert sands, but I think it's a lot safer where it's drier. If I'm concerned, I'll wash with water instead.