Water stone

No problem, you can go under ground, and if you have the miner's kit (which you will have if you can go underground) you should find the sparkly bits on your map, there will be some if you look around (they appear on your map, go to where they are and you will see them) the white ones on the ground are traps 'look' at them to get the trap, the yellow ones in the walls are things you can dig. 'look' at them, and then use your stylus to dig in the walls. there will mostly be prisms, but occasionally, you will find water/fire/grass/electric stones, and also fossils and things good to sell, ike nuggets. Look around and you should eventually get one.


Also: you can find one above ground, in sunyshore city.

Try the Underground. It will take some time, but have patience and you'll find one.

Water Stones can sometimes be found Underground.

Route 213, to the right of Pastoria city, got to sea and use surf, just follow the rock barrier until you find the entrance, there are also some trainers there so be careful, of course if you have firered or leafgreen just give one to a Pokemon to hold and then migrate over.

Im sure you can always use Action Replay if you are extremely desperate :P. But I found a couple of water stones in the Underground, but it takes time and patience