My sister has a day care and she has a lot of oak trees. You know, if you tell small people to gather umpteen billion acorns off the ground as some sort of game, they will do it! She ended up with the acorns cleared from her yard, and I ended up with a good crop of acorns this year.
Anyway! One of the products of processing acorns, is tannin water. In order to use acorns for anything but throwing at each other, or decorations, or checker pieces you must leach the tannins out. The tannins in acorns is what makes them bitter and inedible to humans in their raw form (you COULD eat them if you HAD to.. but they would be very very very bitter, and probably give you a belly ache).
I could go into a whole big thing here about how I process acorns, but this is going to be more about the tannin water and the benefits from it.
This water is a tannic acid solution that has a variety of uses. This water is very antiviral and antiseptic and can be used as treatment for many, topical issues. It is great for poison ivy, cuts, rashes, burns, etc. This is what my family has benefited from the most. My mother even used it on the cat! This is the best story. My cat had a hot spot at the base of her tail and she would bite it till the skin was bare and raw. The vets tried everything from topical creams to internal medicines and nothing helped. I gave my mother some tannin water and suggested she try it, couldn't hurt right? She did, and not only did it clear up quickly, it never returned!! When I was on the Trail, I got a decent sunburn. I gathered up some acorns and boiled them up for the water (let it cool), put that on my sunburn and I was good to go!
I have also used it as a detergent for washing clothes (not whites!). It leaves your clothes smelling so fresh! Don't use it on your whites, unless you want to dye them.. in which case it makes a GREAT dye.. but you need to fix it with salt to keep it from fading.
Things I have yet to try, but have read: it can be used as a gargle for sore throats, taken as a mild tea for diarrhea and dysentery (good to know when hiking!), it can also be used externally for hemorrhoids.
Of course, what tannic acid is best known for is tanning hides (how tannic acid got its name... or was it the other way around? ). I have yet to take advantage of this use, but perhaps some day?