John, you can drink the water in SJdC. I was one of the few gringos living in SJ in the late '70's. Operated heavy equipment grading the spots for resorts, pipelines and even the golf course when FONTOUR, the Mexican tourist development agency, poured millions into developing the area. I had the only arc welder in the area and became very popular when there was electricity to run it. In the four years I was there it went from a sleepy town to a big city. When the Ford dealership went in that was enough for me!
You'll have a hard time not having a great time. This is the best time of year there, it's spring, the desert plants there are the opposite of here, they lose their leafs for the hot time of the year. It will still be very warm though. Fishing is the best in the world. A couple of my favorite things to do are coast road north from SJ towards La Paz, it was true adventure dirt road when I was there, it may be paved now. There is also a bad dirt road a little north of the SJ airport that cuts over the mountains to the Pacific side that is very beautiful. Have a good time.