Stagnant water can create a breeding ground for mosquitoes. See Section 26-9(a)(12) of Chapter 26, Housing and Building and Maintenance Standards on the attached link for the Code reference. (Bottom of page re: public nuisance)
DHCA Housing Code Enforcement does not have jurisdiction inside the municipalities of Gaithersburg and Rockville. Complaints regarding rental properties within the City of Takoma Park are also handled by DHCA but complaints regarding commercial or owner-occupied properties within the city limits are handled by the City of Takoma Park.
For stagnant water on private property, use the knowledge article, Housing Complaint, or contact MC311 during regular business hours: Monday through Friday, 7 AM to 7 PM.