The only way there could be a spark is A) Static Electricity, B) A potential difference between the pipes (maybe earth ground - maybe not) and House ground. So measure the difference. Disconnect the water pipe and measure the voltage drop between the two. Since the house ground is not connected to the pipes and all wires have resistance there will be a potential difference – hence a spark. Good advise is to check with an electrician and do what your local code allows. You might also want to look into an isolated ground circuit. There are some good discussions here about isolated grounds, if you do a search in the discussion forum and you will find them. – Dan
Sparking Ground Wire
"My electrical panel in my house is grounded to my cold water inlet. I replaced the worn clamp to the pipe and noticed a small spark when I touch the ground wire to the pipe. What could be causing this. My understanding is that the ground should be dead and should have no current. Any suggestions?"