Your best bet is to use a solution to kill the bacteria that might be living in the pot. This happens with steel / aluminum water containers as well, in my experience, so never fear!
According to the official Clorox blog:
It is good your daycare is using bleach for disinfecting, and now you can pass along some information to help them use it correctly! The ¼ cup per gallon dilution they use is more standard as a bleach pre-soak for bleachable fabrics that are heavily soiled or for fabrics that need to be disinfected. It is actually not strong enough to disinfect hard surfaces. Instead, to disinfect furniture and hard, non-porous toys, the correct dilution is ¾ Clorox® Regular-Bleach per gallon of water. You are also correct to note that they should be measuring a full gallon of water that the ¾ cup is then added to, a 1:21 dilution. Items need to have contact with this disinfecting solution for 5 minutes, and then should be rinsed thoroughly and allowed to air dry.
However, the blog also indicates that porous surfaces (I assume your clay is porous) are NOT safe for bleach!
For mopping floors (ceramic tile, vinyl, linoleum—not marble or other porous surfaces that aren’t safe for bleach), mix up a solution of ¾ cup bleach added to 1 gallon of water. For disinfecting, wipe or wash the floor, then apply the bleach solution and let stand for 5 minutes. Rinse well and air dry. Also, be sure the area is well ventilated while you are working.
Instead, I would use hydrogen peroxide. It's inexpensive, readily available at drugstores, and it's a weak acid. The pharmacist should be able to help you dilute it properly, if necessary, though it likely won't be; drugstore hydrogen peroxide is a 3% dilution, and it breaks down in sunlight anyway. In addition, it is much stronger when mixed with vinegar, which most folks have in their homes anyway. Remember: ACID TO WATER!