Gearbest has Aqara Smart Water Sensors on a flash sale for $9.99 plus shipping. Can be configured to work with SmartThings hub (it is not the easiest to do). Note that mine are showing up in SmartThings Classic Android App but not the latest SmartThings app. I used device handlers found on GitHub after reading posts about these sensors in SmartThings Community.
https://www.gearbest.co