Holbrook, NY Cesspool & Septic: Sewer, Rules, Grants

Short answer: Only part of Holbrook is sewered.

Holbrook in numbers

Town	Town of Islip (Brookhaven 16% elsewhere)
Area	6.88 sq mi
In active sewer district	23% · Parkland Sewer District, Birchwood Sewer District
In proposed district	4% · Oakdale Phase 7, Holbrook Study Area: Extension to Sewer District 14
Groundwater zone	Zone I 94%, Zone VI 6%
FEMA flood zone	0%
One-family lots / median	6,144 / 0.24 ac
One-family lots outside active sewer districts	about 4,761

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

Only part of Holbrook is sewered. The county layer puts about 23% of its area inside Parkland Sewer District, Birchwood Sewer District; homes outside that line use on-site systems. A sliver (4%) is inside a proposed district (“Oakdale Phase 7”, “Holbrook Study Area: Extension to Sewer District 14”). By parcel count, roughly 4,761 of Holbrook's 6,144 one-family lots sit outside an active district; that is the local cesspool and septic population, before counting unconnected lots inside districts. Next door: Holtsville (8% sewered, median lot 0.34 ac); North Patchogue (0% sewered, median lot 0.20 ac); Lake Ronkonkoma (0% sewered, median lot 0.23 ac). By active-sewer share Holbrook ranks 23 of the 165 Suffolk hamlets and villages we measured.

Groundwater, lots and flood exposure

Groundwater management Zone I (94%) and Zone VI (6%): 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 6,144 one-family lots touching Holbrook, with a median of 0.24 acres (about 10,700 sq ft), below that minimum and the 129th-largest median lot in our Suffolk table. No part of Holbrook is mapped in a flood zone of note, a groundwater protection area or the Pine Barrens.

For most Holbrook 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 Holbrook

Building and electrical permits: Town of Islip
Sewer: Parkland Sewer District
System approvals and grants: SCDHS, 631-852-5700 (permits) / 631-852-5811 (grants)

Frequently asked questions

Is Holbrook on public sewer?

Partly: about 23% is inside Parkland Sewer District; the other 77% relies on cesspools, septic tanks and I/A systems.

Can Holbrook 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 Islip overview, septic grants, replacement rules. More in Islip: Bohemia.

Sources

Each source was re-read on November 7, 2026. Program amounts and rules change; the agency page is the authority.

Need cesspool or septic work in Holbrook?

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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