Though the poet Thomas Gray wrote a famous poem on the drowning of a pet cat , cats rarely do drown because they can swim when they have to. If they fall into a pool or large tub that they can’t climb out of, then of course swimming won’t save them.
A cat who has “gone down for the third time” but is still alive can be aided by being held up by the hind legs, which will help get most of the water out of the lungs. Naturally the nearly drowned cat needs a vet’s attention as soon as possible. While drowning is unlikely to happen to your cat or any other, it would seem to be the most horrible kind of death, given cats’ notorious aversion to water.