Septic & Wastewater Questions

You will need to submit a land research request form, and an environmental health specialist will be in contact with you once the research is conducted. At that time, environmental health will provide guidance on how to move forward with your project.

A COSA, or Certificate of Subdivision Approval, is a document created by the Montana Department of Environmental Quality (DEQ) when a parcel is divided into parcels smaller than 20 acres. This applies to all divisions of land, not just those on named subdivisions. This document contains approval for wastewater facilities on each lot within the division.

If your property is under 20 acres, you may submit a land research request form and request a copy of the COSA. Be specific about your plans for the property to ensure you get the best response.

If you have an existing home connected to city sewer or with a valid septic permit, you may apply for a vacation rental license on the Environmental Health sleeping accommodations page.

If you want to construct another dwelling to rent as a vacation rental, first determine whether your property is approved for a second dwelling by submitting a land research request form. You will also need zoning approval from the Flathead County Planning and Zoning office.

If your property is approved for a second dwelling, you may submit an application, and the department will check whether your existing septic permit is sized for the dwelling or whether a separate system is required.

If an approved public municipality or sewer district sewer line is readily available within 200 feet of the property line and the owner (publicly owned entity) approves the connection, the applicant must connect. A connection is considered not readily available if:

1. The cost of constructing the connection to the public sewer is greater than three times the cost (3:1 cost analysis) of installing an onsite wastewater treatment system that could be approved for the site. Construction costs only: costs related to annexation, such as road improvements and sidewalks, are not relevant to the determination.
2. Connection to the public system is physically impractical.
3. Necessary easements cannot be obtained.
4. The publicly owned entity is notified of the department's decision and concurs with the septic system installation or repair approval.

It is best to receive septic approval before drilling your well. Sometimes environmental factors may limit the locations of your septic system.

It is advised that you get septic approval before building your house. Sometimes environmental factors may limit the locations of your septic system.

Please refer to the Flathead County Septic Regulations.

Please refer to the Flathead County Septic Regulations.

Systems installed near a floodplain must meet all required setbacks. Additionally, please contact the respective Planning and Zoning office for more specific guidance:

• Flathead County: 406-751-8200
• City of Kalispell: 406-758-7940
• City of Whitefish: 406-863-2410
• City of Columbia Falls: 406-892-4384

Contact your local water district to see if you can connect to city water. If you cannot, the Montana Department of Natural Resources and Conservation (DNRC) Opens in a new tab. must be contacted to obtain water rights to drill a well. If you have a previous approval (COSA) on your property — most properties under 20 acres — be sure to install the well in the approved location.

First, determine whether your property is approved for a second dwelling by submitting a land research request form. You will also need zoning approval from the Flathead County Planning and Zoning office.

If your property is approved for a second dwelling, you may submit an application, and the department will check whether your existing septic permit is sized for the dwelling or whether a separate system is required.

If you add an addition, make sure the total new number of bedrooms complies with the number listed on your existing septic permit. You can look up your existing permit on the Flathead County GIS Interactive Mapping Portal Opens in a new tab.. If you cannot locate the permit on GIS, submit a land research request form.

If you want to create a shop apartment, first determine whether your property is approved for a second dwelling by submitting a land research request form. You will also need zoning approval from the Flathead County Planning and Zoning office.

If your property is approved for a second dwelling, you may submit an application, and the department will check whether your existing septic permit is sized for the dwelling or whether a separate system is required.

If you notice that your septic system is failing, fill out a land research request immediately and state in the request that your septic system is failing.

Constructing a single RV site is considered adding a dwelling to your property. First determine whether your property is approved for a second dwelling by submitting a land research request form. You will also need zoning approval from the Flathead County Planning and Zoning office. If your property is approved for a second dwelling, you may submit an application, and the department will check whether your existing septic permit is sized for the dwelling or whether a separate system is required.

Constructing two or more RV sites requires Subdivision Review. You will need to hire a consultant or engineer — see the consultant and engineer list in the Quick Links on the Sewage and Septic page — to submit the subdivision form to the DEQ and perform the required environmental analysis and design. After the subdivision is approved by the DEQ, you may submit an application for a septic permit to the county.

You should first submit a land research request form and ask "what is my property approved for?" Be specific about your intended plans for the property.