Anyone who lives in the D.C. region and relies on clean drinking water to live — in other words, everyone who lives in the D.C. region — needs to be aware of a debate that’s about to come to a head in Montgomery County.

A proposal to amend the land-use plan for the Clarksburg area, in the northern part of the county, is set to be taken up by the county council in December. This proposal may endanger the integrity of the water system for metropolitan Washington by permitting millions of square feet of commercial and office development and the construction of hundreds of residences alongside the headwaters of Ten Mile Creek, the last undeveloped tributary of Little Seneca Reservoir.

As former Montgomery County officials, each of us was involved in the creation of the reservoir and its designation as a key component of the water system for metropolitan Washington. It supplanted massive and ill-conceived alternatives, including a proposal to place some 16 dams on the Potomac River that would have inundated most of the C&O Canal and destroyed the character of the river basin. Regional leaders discovered that in the event of a drought, with an appropriate regional system of interconnected local water supplies, Little Seneca Reservoir alone could sufficiently augment the flow of the Potomac until water released from another, larger reservoir reached intakes in the river.

This new regional water supply system, with Little Seneca Reservoir at its core, was formalized in the 1982 Water Supply Coordination Agreement, signed by the region’s major water utilities in Maryland, Virginia and the District and the Interstate Commission on the Potomac River Basin.

But the integrity of that system is now threatened. The development blueprint approved by the county Planning Board in October concedes that development of any scale would degrade Ten Mile Creek; the only questions are by how much and what effect would this have on the reservoir. We don’t know the answers to these questions because no comprehensive study has been carried out. Notably, the Planning Board’s professional staff recommended a level of development well below what the board approved — and even that lower intensity involved significant risk. The board then increased the level of development recommended by its staff by 50 percent east of Interstate 270 and 300 percent west of the highway. No justification for this level of damage is offered in the plan.

To approve such expanded development without a careful, professional and independent analysis of its impact on this critical water resource would constitute an abandonment of the stewardship responsibilities that the county exercises for the 4.3 million people whose water is drawn from the Potomac.

We have walked in the shoes of planners and council members and understand the difficulty of making decisions that are certain to disappoint some interested parties. We share responsibility for the present problem because 30 years ago, when we proposed and acquired land for the reservoir and helped to negotiate the agreements for its role in the regional system, we should have taken stronger action to ensure its protection. But we did not anticipate that future planning boards and county councils would consider massive development along the headwaters of the reservoir without first carefully studying the damage it could do to the region’s water supply.

We believe the responsible course for the Montgomery County Council to take at this point is to drastically reduce the proposed density and impervious-surface limits in the Clarksburg amendments. Better yet, reject the plan and remand it to the Planning Board for reconsideration after a thorough, independent analysis.

John Menke was a member of the Montgomery County Council from 1974 to 1978 and later served as director of the county Department of Environmental Protection. Scott Fosler served on the county council from 1978 to 1986. Royce Hanson was chairman of the Montgomery County Planning Board from 1972 to 1981 and 2006 to 2010.