ground wire bridge on copper pipes

If you are in an apartment complex, you should ask the apartment superintendent or owner first. That's their responsibility.

That being said, is it a ground wire for the entire electrical system or is it a water heater bonding wire jumpered between the hot and cold water pipes?? sounds like to me it's a water heater bonding wire as you state it's on every water heater. Please post a picture. thank you.

If it is a water heater bonding wire, local codes may still require it. Idk. Check with your local municipality for local codes information. They should be able to answer your question.

The management is using good risk management but should have taken it a step further. To be sure you are safe from any possible fault current between the water pipes they should have told you to not hold both of them at the same time unless you put the bonding back somewhere else. It's not likely you'd be in danger but it's their insurance that will have to pay if you get hurt and they neglected to tell you the safe way.

Perhaps they told you all that and you didn't post their complete instructions.

The bond wire is necessary since the water heater has dielectric isolation fitting which stop the normal flow of current in the water line. I suspect they told you to put it back when you finish.