What to do, or how to do it?

Here’s the story:
I received a water bill in the mail today from my first rental property. Part of the lease agreement states that the tenant will pay all utilities. Apparently, the couple did not change the billing address with the city. (The water and electricity were on upon their arrival. However, they changed the billing address for the electricity but not the water.)What should I do in this situation? Will a letter suffice?

Call them and tell them that they MUST pay you the water bill with the rent this month and that they must immediately switch the water into their name. If they don’t, get rid of them.