>This is plain water,
How the heck do you know that, and what exactly is "plain water" anyway?

I mean, you go to Saint Petersburg and see water coming out of the tap that looks just like the water in your tap at home. But it's not, you drink it and you get the runs.

In the US we have all kinds of problems with things that were imported unofficially (or unknowingly), like the python in Florida, kudzu in North Carolina, carp in Illinois, the beetle that killed all the chestnut trees. Who knows what is in your water and what your friend will do with it when she gets bored with this hobby. I would not do what you are thinking of doing, out of ecological considerations.

Maybe go ahead and boil the water for 10 minutes or so to make sure it contains no living contaminants. I don't know even if this will work, I am not a scientist.