The short version
For most Suffolk homeowners whose cesspool needs replacing anyway, the question isn’t “I/A or nothing.” It’s “I/A with grants, or conventional with no grants.” Framed that way, the I/A system often wins on cash out of pocket. It loses a little on ongoing costs.
Worked examples
These are illustrations using the published caps. The County decides real amounts, and every site is different.
| Conventional septic | I/A, typical | I/A, expensive site | |
|---|---|---|---|
| Installed price | $20,000 | $36,000 | $52,000 |
| County SIP grant | $0 | −$20,000 | −$20,000 |
| NYS SSRP (75%, max $25,000) | $0 | −$16,000 | −$25,000 |
| You pay for the install | $20,000 | $0 | $7,000 |
| Plus (all options) | Design and permits if needed | Design-professional fee and anything the County won’t count | Same |
In Southampton, East Hampton or Shelter Island, a town rebate can cover some of what’s left on the expensive site. Try your own numbers in the grant estimator.
The costs people forget
Design fees
For a grant job, you hire a design professional at your own expense, who files the plan with the County Office of Wastewater Management. Ask installers whether their price includes design, permits and County filing, or whether it’s separate.
Maintenance
The County SIP grant funds the first 3 years after installation. After that you need an annual contract with a licensed I/A maintenance provider. The Peconic Estuary Partnership estimates about $300 a year, and it has announced a reimbursement of up to $500 a year for homes in its area (check that it’s open before counting on it). Over 20 years, that’s roughly $5,000 you wouldn’t spend on a conventional system (minus the pumping a conventional system needs).
Electricity
I/A units run a small blower or pump continuously, so there’s an electrical hookup and a modest ongoing electric bill. Ask the installer for the specific unit’s power draw.
Taxes
Good news here. The IRS said in 2020 that Suffolk’s grants were taxable, but reversed that in November 2022 (Announcement 2022-26): County SIP payments aren’t included in homeowners’ gross income, and the County doesn’t issue 1099s for them. The announcement covers the County payments, so ask a tax professional about the State and town portions. (Nassau’s program materials say its grants aren’t taxable either.)
When conventional still makes sense
- Your street is in a sewer district or a proposed one. No septic grant, and sewers may be coming.
- The system has failed and you can’t wait for the grant to be issued (the grant must come before installation).
- You don’t meet eligibility: no valid Certificate of Occupancy, unpaid taxes, or the deed isn’t recorded in your name yet.
When I/A is a no-brainer
- You’re in Southampton, East Hampton or Shelter Island, with town money on top.
- Your site is straightforward and the installed price is under about $45,000, where the County and State caps can cover most or all of it.
- You’re planning a renovation that counts as major, which will require an I/A system anyway.
Next step: get an approved installer’s real price and plug it into the estimator.
Need it done? See i/a nitrogen-reducing septic systems on Long Island. Town grants & sewer districts: Southampton, East Hampton, Shelter Island.
Sources
- Suffolk County Septic Improvement Program page: SIP up to $20,000, SSRP up to 75%/$25,000
- Suffolk County SIP Homeowner Process Overview (2026): design professional at homeowner's expense
- Peconic Estuary Partnership: I/A maintenance fact sheet (≈$300/yr; up to $500/yr reimbursement)
- IRS Announcement 2022-26: Suffolk SIP payments not included in gross income
- Shelter Island Reporter: I/A costs $35,000–$40,000, $50,000+ with extras
- Town of Southampton I/A OWTS Rebate Program