What Is a Nitrogen-Reducing (Enhanced) Septic System?

A nitrogen-reducing septic system, which Florida law calls an enhanced nutrient-reducing (ENR) onsite sewage treatment and disposal system, is one approved to remove at least 50% of the nitrogen in wastewater before it reaches the drain field, or at least 65% counting the tank and drain field together (s. 381.0065(2)(f), F.S.).

Explanation

Florida requires ENR systems in what DEP calls "impacted areas": places covered by a basin management action plan (BMAP), a reasonable assurance plan (RAP) or a pollution reduction plan (PRP). Some springs plans set stricter septic rules of their own.

When Florida requires one

• New systems, small lots: since July 1, 2023, a new system on a lot of 1 acre or less in a BMAP, reasonable assurance plan (RAP) or pollution reduction plan (PRP) area must be nitrogen-reducing where sewer is not available (DEP).
• Silver and Rainbow springs (largely Marion County): DEP adopted this springs plan by final order on June 27, 2025, and declared it final and effective on April 27, 2026. Repairs on any size lot in the plan area need an ENR system, and DEP's August 2026 table lists the any-lot-size rule for new systems as of July 27, 2026.
• Wekiwa and Rock Springs (Orange County): since March 1, 2025, repair and modification permits on lots under 1 acre in the Priority Focus Area require an upgrade to a system with at least 65% nitrogen reduction.

Rules differ by plan area, so check yours with your permit office or the county resource finder.

Which systems qualify

DEP lists 3 kinds of system that can meet the ENR standard:

• In-ground nitrogen-reducing biofilters (INRBs): layers of media installed under the drain field that act as a biological filter. Rule 62-6.009(7), F.A.C., sets a target of at least 65% removal of total nitrogen.
• Nitrogen-reducing aerobic treatment units: only Florida-approved units certified to NSF Standard 245. Not every ATU qualifies.
• Nitrogen-reducing performance-based treatment systems approved in Florida.

When to seek help

• You are building on a lot of 1 acre or less without sewer. Ask the permit office whether your lot is in a plan area.
• Your system needs a repair and you live in the Silver and Rainbow springs plan area (largely Marion County) or the Wekiwa Priority Focus Area in Orange County.
• You are buying a home in a springs area. Ask what system is installed and what a future repair might require.
• You want help paying for an upgrade. Orange County runs a septic upgrade program for the Wekiwa and Rock Springs area; ask your county what is open now.

Learn more in springs protection and nitrogen-reducing septic systems, conventional vs. aerobic septic systems and Florida septic regulations. For funding, see septic repair assistance and financing, or compare septic installation companies.

Related terms

• Aerobic treatment unit (ATU)
• Drain field (leach field)
• Percolation test
• Mound system