I've used a variety of other liquids instead of part of all of my water. Now that I master batch my lye (with water at 50% concentration), I tend to use only partial water replacement, however. But before I started masterbatching my lye solution, I often used a full replacement.
Coffee was the first liquid I used in place of plain water for making soap. My husband loves coffee soap and I was very disappointed that the smell of coffee doesn't carry through into the soap. So I went in search of a good coffee fragrance oil. '
Tea was the next liquid I used as I am an avid tea drinker and have an abundance of teas from which to choose. Marshmallow tea was probably my first tea I used to make soap (made with dried marshmallow root.) Mostly it is useful for coloring the soap tan, as nothing much survives the chemical changes that happens when it interacts with lye.
Kombucha Tea was for my SIL, who is very fond of the tea and cultivates her won Kombucha tea. Others besides my SIL have used this soap and I get positive feedback on it. I'm sure it's more about the sugar in the tea than the tea itself that makes the soap bubbly, and that it's a 'label appeal' thing going on.
Beer tends to make a very strong odor when mixing the lye solution, but some people really seem to like the idea of Beer Soap. The smell sticks to the soap for awhile, but eventually mostly mellows. Some people say the smell goes away, but I can still smell a faint hint of beer or hops over a year later.
Aso aloe, coconut milk, buttermilk, goats milk, carrot juice, tomato, vinegar, and I'm sure some others that are not currently coming to mind, have all been used in my soaps. Egg yolk is my actually my favorite addition to soap. It's not something to replace all water, obviously, but when using tempered egg yolk, it does replace some of the water. I think buttermilk is another of my favorites, but that's more about the fact that I just love buttermilk.
I also like using vinegar in soap, but found that it cannot be a 100% water replacement. Too much vinegar made my soap brittle and it would fall apart when cut if I waited too long. Perhaps it was more an issue with timing when I cut the soap as opposed to using too much vinegar. But for me, the solution was to use less vinegar. It helps harden the bars up quite nicely.
I understand about not wanting to smell something that doesn't appeal to you. I felt that way the first time I soaped with lard. I am not in the least fond of the smell of lard. I'm not particularly fond of the smell of beer or wine, either. Probably why I've only made beer soap once and never made wine soap at all.
Oh, and I have read about people using potato water (I think here on this forum in an old thread) and want to try that someday myself. It occurred to me that if one can use potato water, what about pasta water or rice water? All seem feasible, but I have yet to experiment with them myself. I tend to make soup with my pasta water, and I almost never boil potatoes, and since I don't make congee much anymore, haven't had any rice water around to use in soap. Still, it may be interesting to see what the soap would be like. I read that those who do the potato water soap seem to really like it.
