to get a water stone you need to find a blue shard and give it to the man in the house about half way beetween lilycove and mossdeep. (NOTE-to find a blue shard you need HM dive to dive under water.)
Exchange Blue Shard with the Waterstone. You'll find waterstone in Abandoned Ship, too.
Dig it out in the underground.
Yes the only way you can get a starmie is by usinga waterstone on a staryu.
You can buy it at the Cleadon department store
Pokemon ruby's version IS Pokemon ruby.
You can find it somewhere or you can go underground and dig it up.
Yes, you can dig up a waterstone in Pokemon platinum underneath the resort area.
For which game? Pokemon Red Pokemon Blue Pokemon Yellow Pokemon Gold Pokemon Silver Pokemon Crystal Pokemon Sapphire Pokemon Ruby Pokemon FireRed Pokemon LeafGreen Pokemon Emerald Pokemon Diamond Pokemon Pearl
You must evolve the Eevee you get from Celadon City with a Waterstone.
Poke'athalon
Arceus is not possible to find in Pokemon Ruby. It was released in 2007 with Pokemon Diamond and Pearl
only vapreon