Private Well & Septic Service
Access to the Department of Permitting Services
If you have arrived at this webpage because you have:
- A problem with your well or septic system,
- A problem with a neighbor’s well or septic system,
- A need for information about well and septic system testing and permitting requirements.
Please contact the Well and Septic Section in the County’s Department of Permitting Services (DPS). Call "311" (240-777-0311 from outside the county). You can also visit the DPS website.
Onsite Systems Management Program
The Onsite Systems Management Program (OSMP) is intended to provide owners of wells and/or septic systems with information about the operation and maintenance of these onsite systems.
- View additional information about Onsite Systems Management Program
- Register for the Onsite Systems Management Program
To see mapping of well and septic tank locations for your property, visit the mapping application. Note that this data is currently limited to onsite systems permitted before 1997. (Additional onsite system locations will be added in the future.)
OSMP Legislation Update
In October 2021, the County Executive transmitted to the County Council proposed legislation (Bill 40-21, Individual Water Supply and Sewage Disposal Systems – Amendments) related to DEP’s Onsite Systems Management Program for wells and septic systems. The proposed legislation will 1) require that property owners having a septic system pump out the septic tank at least once every five years, and 2) provide for a partial reimbursement for the cost of the pumping. The Council held a public hearing on the legislation on November 30, 2021. A Transportation & Environment (T&E) Committee work session is pending.
Onsite Systems
When your property uses a well for drinking water supply and a septic system for wastewater disposal, you essentially become your own sanitary utility. You own and operate the facilities, maintain them, and must replace them when necessary. We use the term “onsite systems” to refer to private water supply wells and private septic systems collectively. The State of Maryland also refers to these as "individual systems".
Your water supply system is the well drilled into ground beneath your yard. The well taps into and collects the groundwater in the rock strata under your property, which you then pump out for your use. Your wastewater disposal system is the septic system buried elsewhere under your yard. The septic system treats wastewater that flows from your home or business and disperses partially treated effluent into the ground for final treatment as it percolates through the soil.
The ability of these private systems to provide fresh water and dispose of sewage depends on the soil and rock conditions under your property and on how well you maintain and operate the systems.
Onsite Systems Distribution in the County
The Department of Environmental Protection (DEP) estimates that approximately 17,500 properties in the county use an onsite well for their water supply. Approximately 20,000 properties use a septic system for wastewater disposal. Most of these onsite systems are found in large-lot residential and rural-zoned areas. As shown on the following maps, areas served by onsite systems tend towards the western and northern parts of the county. However, numerous onsite systems still serve properties within the existing public water and sewer service areas, including locations where public water and sewer mains are available for service.
Montgomery County Public Water Service Areas and Well Locations

Montgomery County Public Sewer Service Areas and Septic System Locations
Onsite Systems Testing & Permitting
When a property owner has a well or septic system installed for use on the land, the owner wants assurance that they will function adequately and provide service for a reasonable length of time. The testing and permitting requirements established by the County's On-Site Systems Regulations ensure that when wells and septic systems are installed that purpose is accomplished.
In Montgomery County, the Department of Permitting Services (DPS), acting on behalf of the Maryland Department of the Environment (MDE), has the responsibility of testing for and permitting wells and septic systems. (Note that in other Maryland jurisdictions, the local Health Department often carries out this function.)
The discussions below on the testing and permitting processes for wells and septic systems provide only general background information. The DPS Zoning Division webpage has well and septic system testing and permitting requirements and application forms. The DPS Well and Septic Section may be reached by phone locally at “311,” or from outside the county at 240-777-0311.
Water Supply Well Requirements
In most areas of the County, groundwater is reasonably plentiful provided you drill deep enough to find it. As a result, DPS does not usually require testing before it issues a permit for drilling a water supply well. However, the agency does need to approve an on-site system plan before issuing a permit.
Flow testing is required after drilling and before a building permit is issued to ensure that the well can pump an adequate flow of water. The state's minimum flow requirement for approving a new well for use is 1 gallon per minute (GPM). Keep in mind that though allowed, 1 GPM is a low flow rate that requires spacing out typical high-volume water uses, such as bathing and washing clothes and dishes, throughout the day. A well producing 1 GPM water flow would produce approximately 1440 gallons of water per day. DPS staff can advise well permit applicants about special requirements, including the areas of the County where prior testing is required for a permit (call 240-777-0311).
The MDE Water and Science Administration's Water Supply Program requires some multiple-unit residential projects and nonresidential projects using groundwater wells to apply for and obtain a water appropriation and use permit. Contact the MDE Water Supply Program.
- Download a copy of the MDE water appropriation and use permit
- Find additional information on how to apply for the water appropriation and use permit
Septic System Requirements
Before any formal testing occurs, the Department of Permitting Services needs to review and approve a layout plan for the site showing proposed testing locations. Following this step, testing for new septic systems occurs in two stages—a water table test and a percolation test.
Water Table Testing
The first test, the water table test, determines the depth to the groundwater, the fully saturated soil under the property. The unsaturated soil between the bottom of the drainfield trench and the top of the water table provides area for treating the wastewater effluent. If a depth of at least approximately four feet-between these is not maintained, untreated wastewater effluent might enter the water table and could contaminate ground water and from there, water wells or streams and ponds. The level of the water table fluctuates throughout the year. Note that this test is conducted only in the late winter to early spring when the water table is known to be at its highest level. If low rainfall conditions have occurred throughout the preceding year, the DPS Well and Septic Section may choose to shorten the usual testing period.
Illustration of Groundwater and the Water Table
Illustration Source: U.S. Geological Survey
Percolation Testing
The second test, the percolation test, determines how quickly wastewater effluent will move downward through the soil. You need to complete and satisfy water table testing before moving on to percolation or "perc" testing. If the flow rate though the soil is too fast, the effluent won't stay in the soil long enough for adequate treatment, again allowing untreated wastewater into the water table. If the flow rate is too slow, the soil won't accept and distribute effluent flows from the drainfield quickly enough. Eventually the septic system will back up to the yard above the system or into the user's building. As expected, either situation can create a public health problem.
Area Requirements
Under current standards, a septic system for a new building lot must have an initial drainfield and enough area for three reserve or back-up drainfields. These back-up fields are built and put into service only as the drainfield currently in use fails. A typical single-family house needs an area of at least 10,000 square feet (slightly less than one-quarter acre) for the initial and reserve drainfields.
Properties in the Patuxent River watershed, with water supply reservoirs for the Washington Suburban Sanitary Commission, must reserve an additional 70 percent for treatment area. That means a single-family house that needs to reserve 10,000 square feet elsewhere in the County would need to set aside 17,000 square feet (slightly less than two-fifths acre) in the Patuxent River watershed.
Septic systems may not be located closer than 100 feet to any existing or proposed well and need to be down grade (lower in elevation) than other nearby wells. In addition, County onsite systems regulations establish other septic system setbacks for site features like steep slopes, stream buffers, and buildings.
Exceptions for Onsite Systems Use in Public Service Areas
Where properties are planned for public water and sewer service, the County’s expectation is that owners will pursue service from public systems if an onsite well and/or septic system fails or if new development or redevelopment is proposed. However, not all properties within the County’s planned public service areas have direct access to existing water and sewer mains. Onsite work for public service for some properties may involve restrictive complications or excessive cost. An onsite system failure may present public and/or environmental health concerns that require expedited relief. A property owner may request the temporary use of an onsite well and/or septic system in these circumstances. Where properties are designated as water and sewer categories W-1, W-3, S-1, or S-3, the Department of Permitting Services (DPS) will require an exception from the Department of Environmental Protection (DEP) that allows for the use of either a new or a replacement onsite system.
A property owner or the owner’s designated representative may request a category 1 or 3 onsite system exception from DEP using this linked application: MS Word version or Acrobat PDF version. Please follow the instructions on the form for completing and submitting the application.
An applicant may find it helpful to discuss their specific case with DEP staff before applying for an exception. Please do not hesitate to contact either of the following staff members for information or with questions:
- George Dizelos at 240-777-7755 or George.Dizelos@MontgomeryCountyMD.gov
- Alan Soukup at 240-777-7716 or Alan.Soukup@MontgomeryCountyMD.gov
DEP does not charge a fee for an onsite systems exception request.
Note that a DEP exception approval does not guarantee DPS permitting of an onsite well or septic system. If DPS does issue a permit for a new or replacement onsite system under these conditions, DPS will likely issue an “interim” permit for the onsite system. Interim permits require that owners of properties abandon the onsite system and connect to public service within a year of the time that public service becomes available. Please refer to DPS Zoning Division for additional information about onsite system permitting issues; scroll down the page to the section titled "Well and Septic".