About 25 years ago I tried the same thing. The daily waste is so large it would need a special filtration system to remove it, and even then you need to deal with the bacteria/virus-contaminated water. Also the waste is so fiberous, it gets hung up on the filter and drain parts. I gave up.
If you figure out something that works in home terrariums without too much daily labor, you could probably sell it on Kingsnake.
In fact, some popular large-ish reptiles are semi-aquatic, such as Dumeril's Monitors and the various water monitors. You might find what you want somewhere in Kingsnake.com You might do a search for water monitor forums for ideas.