At first, the datapack had been created for my minecraft server because there were no other good ones that made water cause damage to a player. However, we didn't use it, so I decided to upload it.
The pack provides the function of causing damage to every player by water, waterlogged blocks, snow, powder snow and filled cauldrons.
Unfortunately, rain is still harmless, because this feature is really hard to make as a datapack feature. Snowballs and water bottles also don't damage players.