How long human can live inside the water without oxygen?

After five to ten minutes of not breathing, you are likely to develop serious and possibly irreversible brain damage.

It really depends on how active they are. If they don't train for their lung compassion they could probably last for about 10-15 seconds. But if they exercise and do their lung compassion exerciser they can hold there breath for about 20-40 seconds and minutes. But you cannot live inside water or else you'll die.