City charging back pay for water to duplex

[Luke Danielson]

Posting for a friend- city is charging them 3 years of back pay due to having a duplex rental (upper/basement) of a single family home that has only one water tap to the house. After the city found out that it has been used as a duplex for 3 years, they charged them back pay for not splitting it up into “2” water sources. Can they do that?