I LOVE these for my tarantulas! Their depth relative to surface area means when you fill it you're good for awhile if you have to be. The evaporation rate is very low even here in TX. I'm disabled and struggle with chronic pain so I do my tarantulas' water once every 7 to 10 days and they never go without thanks to these. They can last longer in a pinch- I ended up bed-bound by an injury for around a month a few days after watering my Ts and when I was on my feet again there was still accessible water for all my girls! Their snug corner fit means my bulldozers don't shove them around, the narrower mouth means less debris get in, feeders are less likely to drown, and my Ts don't seem as tempted to toss a bolas in there, and the low profile makes it possible to keep them by the doors of enclosures like exoterras.