What is it you put in their water...

To make the urine less stinky?? My sister has a new hamster, and her urine is a tad bit smelly. It seems like pine masks the odor better than aspen, but I am highly allergic to pine and cannot use it in her tank. I remember reading that mouse breeders put something in the water bottle that reduces the odor from the urine, but I cannot remember what it was.

Do you think I could do the same for a hamster?? If not, the smell is not too bad- I can deal! Thanks!

I think it's vanilla extract or essence, but I don't know the dosage or if it works for hamsters