Short answer: Sewers barely reach Holtsville: about 8% of the land is inside Birchwood Sewer District, so most homes depend on a cesspool, septic tank or I/A system.
Holtsville in numbers
| Town | Town of Brookhaven (Islip 11% elsewhere) |
|---|---|
| Area | 7.11 sq mi |
| In active sewer district | 8% · Birchwood Sewer District |
| In proposed district | under 1% |
| Groundwater zone | Zone VI 48%, Zone I 30%, Zone III 22% |
| FEMA flood zone | 1% |
| One-family lots / median | 4,118 / 0.34 ac |
| One-family lots outside active sewer districts | about 3,468 |
Computed 2026-11-07 from Suffolk County GIS (hamlet boundaries, sewer districts, groundwater management zones, FEMA flood zones, protection areas, tax parcels). Shares are of land area; a district boundary is not a hookup, and some village-run systems are missing from the county layer. Method and full table.
Sewer coverage
Sewers barely reach Holtsville: about 8% of the land is inside Birchwood Sewer District, so most homes depend on a cesspool, septic tank or I/A system. Counting lots instead of land: about 3,468 of the 4,118 one-family lots touching Holtsville lie outside any active sewer district, and those homes rely on on-site systems. For comparison, the nearest places: Farmingville (3% sewered, median lot 0.28 ac); North Patchogue (0% sewered, median lot 0.20 ac); Holbrook (23% sewered, median lot 0.24 ac). By active-sewer share Holtsville ranks 39 of the 165 Suffolk hamlets and villages we measured.
Groundwater, lots and flood exposure
Groundwater management Zone VI (48%) and Zone I (30%): Article 6's minimum lot for a new home on an on-site system here is 40,000 sq ft in Zones III, V and VI, unless the density is met another way or an exemption applies. County parcel records show 4,118 one-family lots touching Holtsville, with a median of 0.34 acres (about 14,900 sq ft), below that minimum and the 91st-largest median lot in our Suffolk table. No part of Holtsville is mapped in a flood zone of note, a groundwater protection area or the Pine Barrens.
For most Holtsville homes the main running cost is pumping; when a cesspool fails, the replacement must include at least a septic tank, and grants can cover most of an I/A system.
Who handles what in Holtsville
- Building and electrical permits: Town of Brookhaven
- Sewer: Birchwood Sewer District
- System approvals and grants: SCDHS, 631-852-5700 (permits) / 631-852-5811 (grants)
Frequently asked questions
Is Holtsville on public sewer?
Partly: about 8% is inside Birchwood Sewer District; the other 92% relies on cesspools, septic tanks and I/A systems.
Can Holtsville homeowners get septic grants?
Yes, if the home isn't sewered and isn't in a proposed sewer district: up to $20,000 from Suffolk and up to $25,000 from the state.
County rules, licensing and grant steps: Town of Brookhaven overview, septic grants, replacement rules. More in Brookhaven: Farmingville, Medford, Patchogue.
Sources
Each source was re-read on November 7, 2026. Program amounts and rules change; the agency page is the authority.
- Suffolk County GIS Viewer map service (hamlets, villages, sewer districts, groundwater zones, flood zones, tax parcels)
- Suffolk County Sanitary Code, Article 6 (amended 12/1/2020)
- Suffolk County: Septic Improvement Program information
- Suffolk County: SIP property eligibility lookup
Need cesspool or septic work in Holtsville?
Submit a request with your address. We match it to an independent, licensed Suffolk County operator who serves that address; the operator confirms the time and price with you.
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