To reproduce:

1. Create the file saves/<world>/datapacks/disable_water_data_pack/pack.mcmeta with the content »{"pack":{"pack_format":3}}«
2. Create the file saves/<world>/datapacks/disable_water_data_pack/data/minecraft/tags/fluids/water.json with the content »{"replace":true,"values":[]}«
3. Execute /datapack enable "file/disable_water_data_pack".

Result: Water does not act like water anymore in almost all ways, but the FOV still narrows a bit when going into it.