I tablespoon in whatever water you have....no matter how big. Drink immediately, no worries. It will look sort of murky, but it will not have any smell or taste. Let it settle out as you go.
My husband adds a bit more every 5 gallons or so...just to hedge our bets.
Hv said a tablespoon will last for 6 months sitting on the bottom. It will saturate the water. I usually leave at least a couple inches of water before I add more and never let it get to the bottom
The purer the water.....the better.
No need to over think this process...it's all good.