Exterior water faucet required?

[Ken D.]

All my rental properties have water faucets on the outside of the property. My current leases do not have language indicating that car washing, gardening, etc, etc, are not allowed -- but, I know these things are happening because there's always a hose hooked up to the faucet when I come by, even when I've told them not to use the faucet.

Can I put a locking device on the faucet or is there some law (Minnesota) that says the properties must have an exterior faucet (for fire safety, for example)? All my properties were 100% refurbished 3 years ago, and many of them got new exterior faucets during this process -- so I don't understand why the faucets would have been put in if they weren't required when they're such a water/cost liability?