Water has enough surface tension for snails to crawl on while upside down underwater. Laura Hughes writes:
Underwater walking! I found this snail crawling upside down on the water's surface in a small puddle. It's rather incredible if you think about it. Snails take advantage of surface tension and their slimy foot to achieve this. The snail's foot makes little rippling waves and secretes mucus which provides enough grip to walk on the underneath side of water! I sped the video up in some places because although snails can move faster walking on water than on land it's still not that fast. I've seen many aquatic snails do this but I think this might be a terrestrial species maybe Novisuccinea sp. Washington Co. Ohio. 5-17-20.
Here's another example via GrowSeattle:
Image: YouTube / GrowSeattle