Why won't truck start? Changed water pump and now it won't start.

Hello, changing your water pump itself wouldn't cause the vehicle to cease from starting. But it is indeed possible that a step along the way of disassembly and reassembly could have caused a no start condition. See a shop near you if retracing your repair steps yields no results. It would be helpful to know if you have a concern with you have a fuel or ignition system problem. or an emission or air intake problem. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops