Acid Water

Water is no longer safe, in fact it's now one of your most dangerous and constant threats in Minecraft. As this mod makes it so both standing water, whether it be in lakes, oceans, or placed by a bucket, and the rain, will inflict the player and any mob with the wither effect. This makes it so getting caught out in a rain storm will immediately spell doom for your character, and you'll have to use regeneration potions to be able access anything under water making your game significantly more difficult.

FAQ

Q: How do I stop from taking damage in the rain?
A: All you need is one block above your head and you'll be safe from the effect

Q: Are any mobs safe from the effects?
A: Yes, mobs like the Wither who are immune to the wither effect are fine

Q: How can I protect my animals/pets?
A: Just make sure there is a block above their head as well

Q: Can this mod be used in multiplayer?
A: I don't know, I only support single player, but it's possible it can work in MP but I guarantee nothing there.

Notes:

For optimization no water based mobs will spawn, so fish, guardians, squids, etc, will not spawn in, this is just for the vanilla mobs, and will not block modded mobs, the reason for this is performance, and so there's no thousands of items just floating in the ocean for no reason.