Thanks Jon!
It's still code to ground the electrical system to the water system, even gas lines coming in from the street.
The idea is that if they are all connected, it removes the ability for a voltage difference to occur. Voltage difference can lead to sparks, sparks can make heat, heat can make fire. Also the metal pipes that travel outside of the house act as an earth ground for the whole system. Connecting electricity to water and gas is counterintuitive, but it's actually safer.
Bill