How much is a water truck?

Water trucks come in varying sizes and capacities. It could be anything from a truck under 26,000 lbs. GVWR up to a tractor-trailer. Also, there are varying types - some spray water on the ground (to prevent dust from being kicked up in operations such as quarrying or construction), some simply transport water, some discharge it only through a hose.

You'd need to get a little more detailed insofar as criteria goes in order to answer this question. Either way, you'd buy the cab and chassis first, then the water apparatus, or else you'd buy it from a company which has already done this. For a Class 8 straight truck, you'd be looking at probably $150,000 - $170,000, if not more.