Purification

You hold a bit of pure white salt in one hand, and touch any food or water with the other, the piece of food or body of water cannot be larger than 5ft. in radius.
If the food or water is contaminated or poisoned, the salt will absorb it and turn purple.
The GM can allow players proficient in alchemy supplies to make an Investigation skill check to determine what kind of poison or contaminant is captured in the salt.

You can double the radius for every uninterrupted hour of ritual casting.