I did some calculations on how much the leather in a 5 lbs holding waterskin would weigh. I assumed a full waterskin would be a sphere, and used the apparent density of chestnut tanned leather I found in

this article, which is 0.72 g/cm

^{3}. I converted the lbs to kilograms using both the standard lbs->kg ratio of 0.453 and the old Finnish one of 0.425 lbs to kg.

From the results, a 0.3 lbs waterskin with volume for 5 lbs of water would be made of 2 mm thick leather. (The leather weighing 0.27 lbs as standard pounds, 0.28 lbs as Finnish pounds.) The weight increases by about 0.15 lbs for each additional mm of leather thickness. (Averages for the first 10 mm of leather were 0.1417 lbs/mm for the standard pound and 0.1450 lbs/mm for the old Finnish pound.)

I don't know much about leather crafting, but I'd expect a leather waterskin to be made of leather between 2-5 mm thick, meaning the leather of an empty UrW waterskin would have a weight of 0.3-0.75 lbs. Considering that a waterskin would not be a perfect sphere, and it would have a cork and a strap, I'd expect the game's waterskin to weigh between 0.5-1.0 lbs when empty, depending on what thickness the leather is supposed to be.

I don't expect crafting the skin requiring much more leather than it weighs. The extra leather cuts can be used to make a strap. (Maybe the recipe doesn't not need tying equipment at all... Just assume that it's made from the leather while crafting the skin.)

I also read somewhere that the Sami people used to make waterskins out of reindeer leather. Maybe the game's waterskins are based on those, but I don't have a clue what those look like or how they were made.

@GiTiB: Coming up with 4 lbs of leather isn't that difficult either, and a skin isn't that useful of an item. I always make one, but rarely use one.