Montgomery County, MD Landscaping Rules: Rainwater Harvesting (2026)
Key Facts
- Trigger
- Lots under 15,000 sq ft, or +400 sq ft additions
- Design standard
- 1.5 inches of rain in 24 hours
- Qualifying device
- Rain barrel or cistern w/ slow release
- Enforcing office
- Dept. of Permitting Services Director
- Violation class
- Class A violation, County Code § 8-22
Summary
On lots under 15,000 square feet, Montgomery County lets builders satisfy the required runoff-control plan for a building permit with a rain barrel or cistern instead of conventional stormwater infrastructure.
The Director must not issue a building permit for any detached one- or two-family residential building located on a recorded lot smaller than 15,000 square feet... unless the plans provide for safe conveyance or control of any increased water runoff... approved drainage system means any method of safe conveyance from the property or storage on the property of on-site water runoff... using ... rain barrel, cistern with slow release or controlled pump discharge... Each approved drainage system must be designed to convey or control at least 1.5 inches of rainfall during a 24-hour period.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: 2026 S-90: Montgomery County Code contains legislation effective through May 7, 2026 | Zoning Updated Effective: April 13, 2026 | COMCOR Regulations effective as of July 1, 2026).
Full Breakdown
Under County Code § 8-29B, the Director of Permitting Services won't issue a building permit for a detached one- or two-family home on a recorded lot under 15,000 square feet, or an addition that grows lot coverage by more than 400 square feet, unless the plans include an approved drainage system. A rain barrel or cistern with slow release or controlled pump discharge qualifies, alongside rain gardens, bioretention filters, dry wells, and similar devices. Whatever device is chosen must be engineered to convey or control at least 1.5 inches of rainfall in 24 hours, and the owner must certify installation and preserve the system afterward.
Violations & Fines
Building or altering a home without an approved drainage plan, or modifying an installed system without Director sign-off, is a Class A violation of Chapter 8 under § 8-22 and blocks or voids the building permit.
Frequently Asked Questions
Can a rain barrel satisfy Montgomery County's drainage requirement?
Does this rule apply to every home?
Sources & Official References
Other rules in Montgomery County
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