I have lived in Las Vegas for 6 1/2 years, including 7 summers. I'd rather live here than in Florida, where it gets nearly as hot, but which is way more humid and uncomfortable in my opinion. I'm not sure where this idea that Vegas is unlivable in the summer comes from -- it's no worse here in terms of extremes than the winters of some cities. No one would realistically think they could stay outside all the time during the 5-6 month winters of, say, Wisconsin or Vermont. It's already in the high 30's for lows in Wisconsin, for example. But for some reason people accept that without question but think it's crazy living in a place where's it hot (but no shoveling snow!) for 3 months and amazing for 9 months.
As far as Las Vegas getting 90% of its water from the Colorado river, that is true. Which is a whopping 4% of the amount available each year. As bad as things are getting in California, we're not too far from needing desalination there which frees up more than enough water for Las Vegas.
I was born-n-raised, moved to Texas when I was 24 or 25. I've been back a couple times. Dad and sister both live there. Mom and brother are both buried there.
It's pretty damned hot if you're working outside. I don't remember it being that hot when I was younger (we would run across the street in bare feet).
Having lived in both Florida and Las Vegas, Las Vegas is so much nicer. This might be cliche, but the humidity really does make all the difference. High temps are 20 degrees lower in Florida, but I'd rather stand outside in 110F heat in the desert than 90F in a Florida summer.
As far as Las Vegas getting 90% of its water from the Colorado river, that is true. Which is a whopping 4% of the amount available each year. As bad as things are getting in California, we're not too far from needing desalination there which frees up more than enough water for Las Vegas.
More water evaporates from Lake Mead each year (800,000 acre feet) than is used by Las Vegas (300,000 acre feet) -- http://www.usbr.gov/lc/hooverdam/faqs/lakefaqs.html.