Sponge bath lying down in insulated closet is safest option

Even better, there is a way to avoid every risk and save water...

Let me tell you about the flesh-eating bacteria living in your sponge. You better microwave it beforehand.

I've heard in California that will cause cancer.

good that our ancestors didn't know about all this, they would just kill themselves right away sparing us all these enlightening discussions

There is a chocking hazard with the sponge.

Attach it to a 10cm long string with something wide at the other end, so in the event of accidentally swallowing it (and ignoring the "why/how"), you can just pull it out. Problem solved.

Just make sure to not leave it in the driveway and it'll be fine.