Nevada has 4% water rights to the Colorado river. The rest goes to Arizona and California (majority of it goes to farming in desert areas).

https://en.wikipedia.org/?title=Colorado_River_Compact

Nevada plans on getting water from the north and transporting it south...

http://lasvegassun.com/news/2012/sep/12/water-authority-gets...

Regardless, it will be irresponsible to grow a city without access to water.