Where I can find a water stone in Ruby and Sapphire?

Question

I want a water stone for my lombre to become ludicolo.

Answer 1

There are 2 ways to get a Water Stone in RSE.

Abandoned Ship
There is a Water Stone in Room 3, which requires Dive (that's the clearest Bulbapedia is gonna get, huh...)

Treasure Hunter
On Route 124, West of Mossdeep City, there's a single house (you can't miss it). Inside, you'll find a guy named the Treasure Hunter, who will trade you an elemental stone for a shard, depending on what color shard you have (Red shard = Fire Stone, Yellow = Thunder Stone, Green = Leaf Stone, Blue = Water Stone). To get a Water Stone, you will need to give a Blue Shard to the Treasure Hunter. There are 3 ways to obtain a Blue Shard.

• Route 124

Near the southwest corner of the route, via surfacing through the southwest-most Dive spot (requires Dive)

Source

• Route 126

In the bare square among the seaweed in the very southwest (hidden)

Source

• Clamperl
  In RSE, Clamperl has a 5% chance to hold a Blue Shard.

Water Stone acquisition source

Answer 2

Surf south east from Lilycove City, there is a house in the sea which trade many kind of stone from a shard! go to the house, you will see a man called "Shard Hunter", if you give him 1 shard, he will give you 1 stone. Blue Shard for Water Stone, Green Shard for Leaf Stone, ect... so, you can get a Water stone if you trade Blue Shard. Hope this usefull...