Could genetically engineered humans drink seawater?

Obviously this would be quite useful as there are many places where it's hard to get freshwater, and most of the water on the planet is salty. Unfortunately we dehydrate very quickly if we drink it on its own, because our kidneys have to get rid of more water than we would actually take in from the seawater to get rid of the extra salt. This happens because we can only make urine with a certain level of saltiness, because the tubes in our kidneys that concentrate urine, known as the loops of Henle, are of a fixed length. Some animals like the desert rat can drink relatively salty water, as they have very long loops of Henle and can produce very concentrated, salty urine. So if we could find out the genes that affect the length of these loops, I think it's theoretically possible that we could genetically engineer humans with kidneys that can cope with drinking saltier water. But because the kidneys develop very early in life, you'd have to do this while a baby was growing in the womb. And this kind of genetic modification is technically and ethically very difficult to do.