this could become very useful to be able to transport water to water containers without using the canteen. 

This is a great idea and I am all about transporting big quantities of water, however all standing water currently in the game has the prefix 'nasty'.

If we had a way to filter water, or perhaps there was a game mechanic that produced more than a drop of fresh water at a time (rainstorms, turning on the sprinkler, tapping a garden hose, etc), then this idea would be a must have.

If this came to pass, I'd like to be able to add lilypad wax to blueprints (mainly floors and walls, possibly foundations and ceilings) to make them waterproof. Then we could create our own pools of fresh water.

that is a great idea that obsidian should add to grounded.