If you have an old clawfoot bath tub with a standard faucet that’s located inside the bath tub, such as the one pictured at right, you have a potential cross connection. If the tub were to fill up with sewage or something even worse, the household water could come in contact with it, because the spill line of the bath tub is actually higher than the bath tub faucet. If you live in Minneapolis or Bloomington, this is also a required repair for Truth-In-Housing Evaluations.
There are two common ways to correct this issue – replace the faucet or install check valves on the water supply pipes.
A proper faucet for a clawfoot tub will have the opening of the faucet spout located well above the spill line of the fixture, as shown below. I found a small selection of replacement faucets at http://www.plumbingsupply.com/clawfoot.html . The proper faucets are the ones that have the words “Code Style”.
If you like the faucet you have or you just don’t want to change out the faucet, another option is to have check valves installed in the water supply pipes. If you choose this method, make sure the check valves are accessible – when the next home inspector comes through, they’ll probably be looking for them.
Note: If you live in Minneapolis and you choose to undertake either one of these projects, you're supposed to pull a plumbing permit. The TISH handout from the City of Minneapolis specifically says that a faucet replacement does not require a permit, but if you talk to any of their plumbing inspectors or you call 311, they'll tell you otherwise. If you're looking for a better handout, click here Most Common Repairs For Minneapolis
Reuben Saltzman, Structure Tech Home Inspections