Living with a special needs child or adult is never easy. However (and since I've PL-ed in this thread a hundred times, I'll just keep on doing it), I firmly believe it's all in how you raise the child. Get them the proper therapies, teach them boundaries, even given them consequences. Regardless of how 'low' the child is, even a brief consequence, like taking a favorite toy away for a minute after they do something they aren't suppose to will eventually teach them. It's a long, sometimes years long, process and sometimes you have to re-teach, but it's really the only way to ensure some sort of order. Aside from putting them in an institution & throwing away the key.
I've worked with students who absolutely wreck a classroom...like rock star on a bender wreck. The first time I saw this happen, my natural reaction was to attempt to stop the child, but the teacher I was with put his arm out & told me not to, he wants that reaction. Instead, I got the other (special education) children out of the classroom, took them out to the playground & we played a game while the teacher and administrator let that kid wreck the room. When he didn't get a reaction, he stopped. When I got the radio call for the class to come back inside, the teacher was using hand-over-hand to make that student clean up his mess. He was crying and saying "I sorry, I sorry," but he still had to clean up. He threw a fit like that maybe once more, but once he figured out he wasn't getting the attention and had to do the clean up, he stopped.
I realize it's very different when it's your home. My sister (with the severely Autistic son) has a friend who's son (also Autistic), who loves to take the lid off the toilet tank & smash it on the ground until it breaks. As a result, none of their toilet tanks can have lids on them . I know parents who cannot have anything on the walls of their homes, nothing heavy or breakable on the tables because they live in fear of their child and her tantrums. Their home looks like very bare doctor's office. It's so sad. In my opinion, they didn't teach their child (who is now 17) what was acceptable or discipline her when she was younger. But that's just that---my opinion.
In regards to Autistic kids being drawn towards water, my nephew lives up to his zodiac sign of Aquarius. He loves the water, has ever since he was a baby. So you know what my sister did? Got him swimming lessons so he wouldn't drown. If you call any place that offers swimming lessons and explain that you have a child who loves the water, but has special needs, there's usually a program for them or an instructor willing to take them on. My nephew started when he was 3 and by 7, he could jump off the edge of the pool in the deep end & get to the edge of the pool on his own. One skill he had to master was dead man's float, just because it can save you if you can't tread water. Will he survive a shipwreck? Probably not, but then again, most people who aren't strong swimmers won't. But he can have fun in the water & be safe.