On the kits: they cost enough that, unless it's a tiny job, there's no savings in it. Unless it's a tiny job, it's cheaper to get a specialist pro to do it. Do the math: last time I did, the kits were 4 times the price per cu ft.
On water: sure, water's plentiful: but clean water is another thing altogether. I read recently that 40% of the freshwater in America is already considered unsuitable for swimming or fishing (never mind drinking).
As to whether tradesmen realize our work is hazardous: I think so. Most of us are in denial about it, or make jokes about it, but deep down I think most of us do understand. It's not even about the newer products & chemicals; even sawdust'll kill you, eventually. Little known fact: in terms of respiratory cancers, by occupation, carpenters are second only to miners.
But this is where you get into quantity of life vs quality of life. If I had to work in an office, I'd probably kill myself after a few years of it. At any rate, I'd be miserable.
And while my work does expose me to more unhealthy conditions than most people's, it also provides plenty of exercise. I'm 40, and weigh exactly what I weighed in high school. I can still haul 5/8 sheetrock up five flights of stairs by myself, I can still climb up & down ladders all day, or walk around on scaffolds with perfect balance... lots of guys my age can't say any of that, they've been stuck at a desk the last 20 years, and that takes its own kind of toll.