You can dip fruit into an uncursed potion of water to squeeze its juice out and turn it into a (maybe diluted) potion of fruit juice. However, this could be abused if fruit juice is smoky.
Since Grimtooth is permanently poisoned, dipping it in an uncursed potion of water should turn it into a potion of sickness, and dipping it into a pool or moat should turn it into sewage.
The potion of water should always be identified from the start of the game, since “cursed/blessed clear potion” is annoying to read when it’s obvious what the potion is.
Remove holy/unholy water’s ability to bless/curse items. Instead, make blessed and cursed oil serve the same functions. Dipping a stack of uncursed oil in holy/unholy oil will bless or curse the stack, as currently works, but since oil is significantly less easy to get than water, this makes mass-blessing of items harder to accomplish.
Anointing an item with holy or unholy oil ignores effects that would normally happen because of the oil. For instance, dipping an oil lamp in holy oil will just bless it, or do nothing if it was blessed already.
Priests now start with a stack of 4 holy oil.
Water doesn’t get outright removed - other things still dilute to it and turn into it in random alchemy - but it’s not much use anymore except for on-the-go dilution.
Not specified whether you could pray to get a stack of oil potions on an altar blessed, or whether this wouldn’t work.
Dipping Frost Brand into water potions (or possibly any freezing-eligible potion, which is most of them) should freeze and shatter the potion. Likewise for Fire Brand, which should boil potions and ignite (but not explode) oil it’s dipped into.
A minor artifact that turns water into booze. Potentially has an affinity to Priests and they receive it as a sacrifice gift somewhat more often.
Cursed or unlucky wishes for scrolls, potions, or spellbooks may give you the blank counterpart instead of what you wanted.
Dipping water into oil doesn’t count as random alchemy.
Potion of honey; nonmagical but provides a lot more nutrition than juice. Can be obtained from bees somehow, possibly by dipping royal jelly into a potion of fruit juice or potion of water.
When you are polymorphed into a sea monster, you can sit on fountains and drink potions of water to regenerate HP.
New artifact The Phial of Galadriel. It is a potion of water (potion of starlight in dNetHack) that acts as an infinite light source which scares giant spiders and Nazgul that come into it, and can be invoked to bless 1 item. May need more powers to make it better, and behavior for what happens when you drink it, but these are unspecified.
