Spending on make-work projects would probably be GDP negative at this point. The diminishing returns on such projects have probably completely diminished. Everyone has roads, electricity, plumbing, etc.
I recall reading an article about how lots of suburbs underbuilt on infrasstructure and now need new investment, but can't muster up enough political will to impose the taxes needed to pay for it.
(which is relatively specialized work that is happening anyway; it isn't all that specialized, but digging with a machine is incredibly more effective)
Getting rid of lead pipes would do little. Flint is a special case because the city did not add the proper anti-corrosion chemicals to the system when they switched water supplies. Probably every old city in the nation still has lead pipes, but most have properly coated the pipes with treatment so there is little to no lead leaching into drinking water. Of course there are exceptions, but it's not widespread.