Baking soda used for in pools?

Baking soda is used a raising agent in baking. Eg: If you use plain flour for a cake with our self raising flour it will not rise)

Baking soda (called "sal aeratus" in the 1800s) and buttermilk (or milk soured with vinegar or lemon juice) react together to produce carbon dioxide, like baking powder and water, or yeast. This...

Since your question is in the "pool care" section I will assume you mean swimming pool water. In that case, YES, sodium bicarbonate is used to adjust pH and total alkalinity.

Baking soda is also sodium bicarbonate. it raises alkalinty and pH balance of the pool water.

Baking soda can be added to the wash, but it won't take the place of laundry soap. It just helps it work better.