It is our policy to dedicate an engine as a supply for a water tower. (We run no quints) More than likely it will be a third due, or second alarm company that will have this detail. Without exception, we are supposed to reverse lay with our first two engine companies; the first due positions just past the fire building, and the second due backs down the street to supply the first. As such, both of these companies are not able to do any other tasks.
The largest line that we operate on a daily basis is three inch. Water is rarely an issue, even in the inner city where hydrants are nothing more than sprinklers for the neighbors. We are very fortunate to have an excellent infrastructure in place, and most hydrants will give you 60-80 psi. More often than not, you will have two hydrants a block, at a minimum.