There are two ways of getting a water stone:
1) On the abandoned ship there is one inside a pokeball.
2)Dive to the bottom of the sea and find a blue shard then take it to the shard hunters house and he will trade you one for your blue shard.
Hope this helps.
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Water Stone...Well... If I remember correctly, there's a guy who's willing to trade a water stone for a Blue Shard. Oh! And you can find one on the Abandoned Ship.
Abandoned ship, Rm. 2, while trying to get the Scanner after diving.
go underground and look for them
In the Granite Cave at Dewford town. It is not too hard to find it there.
Moon Stone can be found in Meteor Falls, you must get HM07 (Waterfall) before you can get it. :)