They are semi aquatic so they need water most of the time.
do you have a fish tank in your house? Or is there a pond outside your house?
I live in an old building.I don't have one.
It's best to do research before buying a pet. If it needs water, you should get a tank or a pond to provide it. If you can't, maybe it would be best to return it.
Can't I just run water over it in the sink or something?
The water might not be the right concentration of chemicals it needs, and the running water could disturb or hurt it. Researching what you need would be best for the pet. The sooner is the better, if you already bought it.