How do you turn your mermaid sim back into a human?

I think I read somewhere that if the sim doesn't get wet long enough they will turn back into a human.

That's not true. The sim will die if she/he is dehydrated.

They will die if you don't keep them hydrated. You can use the shower/tub or pool as well as going out in rain to hydrate. But you need to stay out of the ocean for 4 days. Then you'll turn human again.

i have been out of water useing cheats to refill my dehydration for 10 days now she is still a mermaid

What are the cheats that you used?

Thanks for lying, cause now my sim freaking died .-.

They will die dont do that

http://www.carls-sims-3-guide.com/islandparadise/mermaids.php this explains everything about mermaids as well as how to turn them safely back into a human sim.