If someone vomits in a pool how long should you wait before the water is clean enough to swim in again?

It does depend on the amount of vomit, size of the pool, and your filtration system. A good rule of thumb is no less than 45 minutes after a contaminate is fully cleaned and the area is super chlorinated. If it is baby spit up I normally tell my guards just to scoop it out real fast but if it is larger and spreads I have no problem clearing the pool in the sake of safety. Remember there has never been a documented case of a bloodbourne illness (hep B, HIV, etc.) being spread through the water.