Hi.
Though it would be very unlikely, it is possible to get pregnant while making out in a hot tub. It would depend on the proximity of your crotch to his lap at the moment of orgasm, as well as the temperature of the water, the positioning of the jets, and so on.
The heat of the water is likely to have killed many of the sperm and the jets would have dispersed a lot of them, too. But the truth is that each ejaculation contains tens of millions of hard-working spermatozoa, whose only goal in life is to find an egg and to fertilize it.
It's probably best not to risk it.
If you want to sit on your boyfriend's lap while making out in the hot tub--or in any other situation in which you are naked or wearing thin clothing--just ask him to warn you if he thinks he's about to ejaculate, so you can move.
Take Care.
