How to Get in the Lower Left Chamber in the Ruins

Call Tully, the fisherman who hangs around Route 42, on a Sunday afternoon for a rematch after you have defeated his Pokemon in battle --- he is the first Pokemon trainer you encounter on Route 42 after obtaining the Mineral Badge in Cianwood City. Use the in-game phone system to set up the rematch, then follow his instructions as to where and when the rematch will take place. After you do this, he may call you at any point in the game and give you a Water Stone.

Speak with Bill's grandfather, who lives in the cottage on Route 25, adjacent to Cerulean City. He wants you to show him different Pokemon in a certain order --- Oddish, Vulpix ("Pokemon SoulSilver") or Growlithe ("Pokemon HeartGold"), Jigglypuff, Pichu and Marill. He gives you a Leaf Stone, Fire Stone, Everstone, Thunder Stone and Water Stone, respectively, for showing him each Pokemon.

Explore the Seafoam Islands in the Kanto Region. The Seafoam Islands are east of Cinnabar Island, which you can reach via Route 21 from Pallet Town. There is a Water Stone hidden randomly in this area.

Compete in Bug Catching contests or in Pokeathlons after defeating the Elite Four and beating the game. Winning Bug Catching contests sometimes rewards you with a Water Stone. You can trade 2,500 points, which you win by competing in Pokeathlons, for a Water Stone on Mondays, Tuesdays, Wednesdays and Fridays at the prize center in the Pokeathlon Dome.

Return to the lower left chamber in the Ruins of Alph once you have a Water Stone in your inventory. Walk up against the sealed wall and open your inventory. Select the Water Stone as you would if you were going to evolve a Pokemon, and the chamber will open.