You will need to consult a local attorney who is familiar with Miami's ordinances, but I would think the city's actions against you, as a property owner, are legal. The city is not a landlord to your tenants, so the state law prohibiting landlords from discontinuing utilities to tenants does not apply.
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You do need to review with this with an attorney. There are number of questions are not really included in your facts. Are the tenants billed directly by the utility or do you provide water service are part of the rent? If you provide the water service as part of the rent and it is cut off because you have not paid the lien, then your are exposing yourself to action by the tenants.
The landlord liable if the landlord is directly or indirectly responsible for the disconnection of any utility (including non-payment of services). In other words the state law does apply.
The tenants have an excellent claim against you for constructive eviction. Get an attorney and fight the water bill and the lien.