The National Electic Code (NEC) REQUIRES that any metal casing be connected to the equipment grounding conductor. This is NOT the same thing as ground rods or the grounding conductor. The casing is grounded, but is not the ground. There is a distinction, that the layman is not expected to understand, but an electrician is required to understand the difference.
In Washington state, pump installers are required to hold both an electrician's license and a plumbers license. We have to take 24 hrs of continuing education every three years. We have to obtain an electrical permit and have the installation inspected by the State Electrical inspector. As a practical matter, they can't inspect what we install in the well, so their inspection starts at the well head, the wiring and conduit from the well to the pressure switch and control box, then to the breaker in the Electrical panel.
My electrical inspector does look for and verify that the casing is grounded. The installation WILL NOT be approved if this is not done. Some steel well caps have grounding screws to accomplish this. Normally I drill a 1/4" hole in the side of the casing, and attach a 2 hole grounding lug to the inside of the casing with a stainless steel bolt and nut. I land the EGC from the pump on one hole, and the EGC from the Electrical supply on the other hole.
I am qualified to obtain an Oregon pump installers license, but have never needed one. Oregon does also follow the NEC, but I don't think inspections are required.