Minn. Stat. § 326B.53: LOCAL REGULATIONS.

Any city, county, or town may, by ordinance, adopt local regulations providing for water conditioning permits, bonds, approval of plans, and inspections of water conditioning installations and servicing, which regulations shall not be in conflict with the rules on the same subject prescribed by the commissioner. No city, county, or town shall prohibit water conditioning contractors or installers licensed by the commissioner from engaging in or working at the business.