Dark: 178 Pokémon resist it, 700 take neutral damage, and 156 Pokémon take super effective damage from it. 0 Pokémon are immune to Dark moves.
Water: 294 Pokémon resist it, 557 Pokémon take neutral damage, and 182 Pokémon take super effective damage from it. The following Pokémon are immune because of their abilities: Shedinja, Poliwag, Poliwhirl, Poliwrath, Lapras, Vaporeon, Politoed, Wooper, Quagsire, Mantine, Mantyke, Maractus, Frillish, Jellicent, Vocanion, Dracovish, Arctovish, Chinchou, Lanturn, Cacnea, Cacturne, Tympole, Palpitoad, Seismitoad, Dewpider, Araquanid, Paras, Parasect, Croagunk, Toxicroak, Helioptile, Heliolisk, Jynx.
Source 1: https://pokemondb.net/tools/type-coverage
Source 2: https://pokemondb.net/ability/water-absorb
Source 3: https://pokemondb.net/ability/dry-skin
Those are the statistics of Water and Dark. They are pretty balanced, but a lot of Pokemon are immune to Water.