Short answer: About 0% of the Town of Shelter Island's land is inside an active sewer district on the county map; about 2,440 of 2,440 one-family lots in the town's hamlets and villages sit outside any active sewer district. The town adds its own septic rebate on top of the county and state grants.
Last updated: November 2026. Data computed 2026-11-07 from Suffolk County GIS; rules and programs re-read November 7, 2026.
Town of Shelter Island in numbers
| Land in active sewer districts | 0% |
|---|---|
| Land in proposed districts | 0% |
| Places with ~0% active sewer | 3 of 3 hamlets and villages |
| One-family lots outside active districts | about 2,440 of 2,440 |
| Groundwater zones (land share) | Zone IV about 100% |
| I/A systems installed (Oct 2024) | about 250, 5% of the county's 5,344; 5th of the ten towns |
| Town septic rebate | Yes |
| Town code on I/A systems | Town code §43-10.4 can require an I/A upgrade during construction review. |
Sewer districts and where the cesspools are
- Active districts: none on the county layer inside the town's hamlets and villages.
By one-family lot count, the most lots outside an active district are in Shelter Island Heights (about 1,400), Shelter Island (about 1,003), Dering Harbor (about 37). Median one-family lots run from 0.91 acres in Shelter Island to 1.70 acres in Dering Harbor. In 0 of 3 places the median lot is smaller than Article 6's minimum for a new home on an on-site system in its main zone. Across the town, about 14% of the land is in FEMA's 1%-annual-chance flood zone.
What the Town of Shelter Island adds
- Rebate: Yes: scored base rebate up to $12,000, plus $5,000 for a pressurized shallow drainfield and $4,000 for a county-mandated well relocation; not for upgrades the code requires.
- Town code: Shelter Island's town code (§43-10.4) can require an I/A upgrade as part of construction review, according to the town's rebate policy.
- Building department: Town of Shelter Island; villages with their own: Dering Harbor.
Every hamlet and village in the Town of Shelter Island
Land-area shares inside county sewer-district polygons; zone = main Article 6 groundwater zone; flood = FEMA 1%-annual-chance zone; lot = median one-family lot (acres). Linked names have their own page. Some village-run systems are missing from the county layer. Full table: sewer coverage by hamlet.
| Hamlet / village | Active sewer | Proposed sewer | Zone | Flood | Median lot (ac) |
|---|---|---|---|---|---|
| Dering Harbor (village) | 0% | 0% | Zone IV | 10% | 1.70 |
| Shelter Island | 0% | 0% | Zone IV | 14% | 0.91 |
| Shelter Island Heights | 0% | 0% | Zone IV | 14% | 0.93 |
County rules apply on top: no cesspool-for-cesspool replacement since July 1, 2019, and an I/A system for new homes and major reconstruction since July 1, 2021. Details, licensing and grants: Suffolk County overview.
Frequently asked questions
How much of the Town of Shelter Island is on sewer?
About 0% of the land in the town's hamlets and villages is inside an active county sewer district, and 0% inside proposed districts; about 2,440 of 2,440 one-family lots in the town's hamlets and villages sit outside any active sewer district. A district boundary is not a connection.
Does the Town of Shelter Island have a septic rebate?
Yes: scored base rebate up to $12,000, plus $5,000 for a pressurized shallow drainfield and $4,000 for a county-mandated well relocation; not for upgrades the code requires.
Who issues building permits for septic work in Shelter Island?
The Town of Shelter Island building department, except in the incorporated villages (Dering Harbor), which run their own. SCDHS approves the sanitary system itself.
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 DHS presentation, 11/19/2024 (hosted by the Town of Shelter Island)
- Suffolk County DHS: Changes to wastewater practices effective July 1, 2019
- Suffolk County: Septic Improvement Program information
- Town of Shelter Island: WQI rebate funding policy (2023-08-01)
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