Treated Water Quality Standards for STPs in India: Discharge Norms Explained

Every sewage treatment plant in India exists to hit a number. Not one number, but a small set of them — the concentrations of pollutants that treated sewage is legally allowed to contain before it can be reused or let go. Get those numbers right and your plant is compliant, your consent is safe, and the water leaving your site is a resource. Miss them and you are exposed to notices, penalties and, increasingly, the personal liability of whoever signed the consent application.

This guide lays out the treated water quality standards India applies to STPs: the parameters that matter, the values you are expected to meet, the crucial difference between discharging to water versus reusing on land — and the genuinely contested history behind the numbers, so you know which figure is solid and which is still argued over.

A discharge standard is a promise the law extracts from your building: whatever comes out of this plant will be clean enough not to harm the drain, river, lake or field it enters. The numbers below are how that promise is measured — but the exact figure that binds you is written into your plant's consent, not just into a national table.

Who sets the numbers, and under which law

Two statutes carry the whole system. The Water (Prevention and Control of Pollution) Act, 1974 makes it an offence to pollute a waterbody, and the Environment (Protection) Act, 1986 — with its Environment (Protection) Rules and their Schedule VI general standards — gives the government power to fix numeric limits. The Central Pollution Control Board (CPCB) frames the standards; the State Pollution Control Boards (SPCBs) enforce them, plant by plant, through the Consent to Establish and Consent to Operate that every STP must hold. If you are unclear how those consents work, start with SPCB approvals for STPs and Consent to Operate; the broader legal map lives in STP regulations in India and MoEF rules for STPs.

The important consequence: there is no single sacred national number. There is a national floor, a much-litigated STP-specific layer, and — the one that actually governs your outlet — the condition your SPCB writes into your consent.

The first question a standard answers: where does the water go?

Indian effluent standards have always distinguished between disposal routes, because a drain that feeds a drinking-water river needs cleaner input than a field being irrigated. The Schedule VI general standards under the Environment (Protection) Rules set different limits depending on destination:

These are the long-standing general standards published by the CPCB — see the CPCB general discharge standards. Read the logic, not just the numbers: the cleanest requirement is for water going into a river you might drink from; the loosest is for water going into a sewer that leads to further treatment. If you only remember one thing, remember that the destination sets the difficulty. For the meaning of BOD, COD, TSS and pH themselves, see wastewater characteristics: BOD, COD, TSS, pH.

The STP-specific saga — and why the number keeps moving

Here is where honesty matters more than a tidy table. The general standards above are the baseline, but from 2015 onwards the government tried to set tighter, STP-specific norms — and the attempt turned into a decade of dispute that is still not fully settled.

The 2015 draft was strict and uniform. The October 2017 notification relaxed it — categorising cities by size and, controversially, dropping numeric limits for COD, nitrogen and phosphorus. That relaxation was challenged before the National Green Tribunal (NGT), which in April 2019 reinstated tighter limits. The MoEFCC appealed to the Supreme Court, which broadly upheld the NGT's authority. Scholars and practitioners have documented this back-and-forth in detail — see this peer-reviewed account of wastewater discharge standards in India and the India Water Portal analysis of the NGT's uniform standards, which also records the expert-committee dispute over whether BOD really needed to drop from 30 to 10 mg/L.

Be careful with the 2019 figures. Different secondary sources report the NGT/CPCB values slightly differently — some as uniform, some as still categorised by city class; TSS in particular is quoted as either 10 or 20 mg/L. That divergence is real, not a typo, and it is exactly why you must not treat any single blog table (including this one) as gospel. Confirm the current, applicable figure against your own consent order and your SPCB's latest circular.

So what must my plant actually meet?

For a private STP — an apartment complex, hotel, hospital, IT park — the operative numbers are the conditions written into your Consent to Operate. In practice, across most SPCBs today, new and renewed consents for treated water that is reused on site or discharged commonly cluster around a "10 / 10 / 50" style specification:

• BOD: ≤ 10 mg/L
• TSS: ≤ 10–20 mg/L
• COD: ≤ 50 mg/L
• pH: 6.5–8.5 (within the 5.5–9.0 general band)
• Faecal coliform: ≤ 230 MPN/100 mL (some consents specify ≤ 100)
• Ammoniacal / total nitrogen and phosphorus: limits increasingly imposed, especially where discharge is to a lake

Treat that list as a strong indicative target, not a quoted statute — your actual limits are whatever your SPCB has written for your site, and they vary by state, by the sensitivity of the receiving waterbody, and by the year your consent was issued. When in doubt, read the consent letter and call the SPCB regional office.

Discharge is the last resort — reuse standards are a separate layer

A point that trips up many facility managers: the discharge standards above apply to water leaving your site. But the whole policy direction in India is that treated sewage should be reused first and discharged only as surplus. Reuse — for toilet flushing, gardening, cooling towers — is governed by its own quality expectations, and the CPCB has issued dedicated reuse guidance. The cleanest sites aim for zero liquid discharge, where effectively nothing leaves at all. The parameter set for reuse overlaps with discharge but adds emphasis on residual chlorine, turbidity and pathogen control; we cover it in treated water reuse standards.

How the number is checked — and what happens if you miss it

A standard on paper means nothing without measurement. Compliance is verified through:

• Periodic sampling and lab analysis of the outlet, cross-checked against your consent limits — the subject of STP performance testing.
• Online continuous monitoring (real-time pH, BOD/COD surrogates, flow) which large STPs are increasingly required to install and connect to the SPCB/CPCB server — see STP environmental monitoring.
• Consent renewal audits, where a track record of exceedances can block renewal.

Enforcement has teeth. Under the Polluter Pays Principle, the NGT has levied environmental compensation on housing societies, RWAs, municipalities and industries running non-functional STPs or discharging untreated sewage. For apartment bodies, this liability is personal and organisational — apartment association STP compliance and the STP compliance checklist walk through staying on the right side of it.

The bottom line

Treated water quality standards in India work as three nested layers: a general Schedule VI baseline that varies by disposal route, a contested STP-specific overlay shaped by the 2015 draft, the 2017 notification and the 2019 NGT order, and — the one that binds you — the specific limits in your Consent to Operate. For a modern building STP, aim for the tight modern targets (BOD ≤10, COD ≤50, TSS ≤10–20, faecal coliform ≤230 MPN/100 mL) and reuse the water rather than discharge it. But because these norms have moved repeatedly and still differ by state, treat every number here as a checkpoint to verify — confirm the current, applicable values with the CPCB and your SPCB before you design, commission or certify a plant.

To go deeper, browse the full Sewage Treatment Plants guide library, revisit how the whole system works in what is a sewage treatment plant, and size your own plant with the STP Capacity Calculator.