Tamil Nadu has promised to defend its interstate river interests, accelerate long-pending water projects and confront pollution in three major rivers. The commitment is strategically important, but the State must distinguish water already awarded, storage rights recognised by courts, projects requiring negotiation and future transfers that remain at planning stage.
Tamil Nadu’s latest Budget places interstate river water at the centre of its agricultural and long-term water-security strategy.
The government says it will enforce timely Cauvery releases, oppose upstream developments that could affect the State’s interests, pursue a higher storage level at Mullaperiyar, implement the Anaimalaiyar and Nallar projects and expedite the Godavari–Cauvery river link. It has also allocated ₹25 crore for feasibility studies and project reports addressing pollution in the Cauvery, Vaigai and Thamirabarani.
These commitments should not be treated as one programme.
They belong to different legal, engineering and financial systems.
Cauvery is the clearest quantified entitlement
The Cauvery Water Disputes Tribunal’s final award, as modified by the Supreme Court in 2018, allocates 404.25 TMC ft to Tamil Nadu. Karnataka is required to make 177.25 TMC ft available at Billigundlu, the interstate measuring point. The Cauvery Water Management Authority and Cauvery Water Regulation Committee were constituted in 2018 to implement the decision.
This is the strongest legal category in the Budget statement.
Tamil Nadu is not merely requesting a discretionary release. It is seeking implementation of an adjudicated allocation through a formally notified management mechanism.
But the annual number can conceal the operational dispute.
Delta agriculture depends on when water arrives. A large release after the critical sowing or transplantation period cannot fully compensate for an earlier shortage. Reservoir storage at Mettur, rainfall within Tamil Nadu and the monthly flow arriving at Billigundlu jointly determine how much irrigation can be supported.
Tamil Nadu’s WRD policy note illustrates the problem. It records that only 81.418 TMC ft was received at Billigundlu during the drought-affected 2023–24 irrigation year, compared with the 177.25-TMC annual interstate quantity. In the following season, Mettur could not be opened on the scheduled June 12 date and was opened only on July 29 after stronger inflows.
The lesson is direct:
annual entitlement without seasonal compliance can still produce agricultural loss.
A distress formula remains essential
The Cauvery framework operates most smoothly in normal rainfall years.
Its hardest test is a deficit year in which reservoirs in Karnataka and Tamil Nadu both hold less water than expected.
Tamil Nadu has repeatedly sought a formal distress-sharing formula through CWMA and CWRC. The State’s policy note continues to list this as an issue requiring resolution.
A credible distress framework should establish:
- the rainfall and reservoir baseline;
- how available water is recalculated;
- monthly proportionate releases;
- treatment of drinking-water requirements;
- crop-season priorities;
- real-time disclosure of reservoir inflows and releases;
- and the process for correcting shortfalls.
Without such a formula, every weak monsoon produces a new political and legal confrontation.
Mekedatu needs precise legal reporting
Tamil Nadu’s opposition to the proposed Mekedatu balancing reservoir is one of the Budget’s most visible positions.
The most recent official Union response, dated July 30, 2026, states that Karnataka’s 2019 DPR was returned to the project authority with instructions to submit a revised proposal compliant with the Cauvery award and current CWC guidelines. The Union government also acknowledged representations from Tamil Nadu and farmers’ organisations concerning delta agriculture and drinking water.
That response contains an important legal qualification.
It says the Supreme Court’s 2018 judgment does not expressly require Karnataka to obtain the consent of Tamil Nadu, Kerala and Puducherry for every structure within Karnataka. It reiterates, however, that Karnataka’s use of Cauvery water must remain consistent with the tribunal order as modified by the Court.
Tamil Nadu therefore does not possess a simple, uncontested project veto.
Its strongest arguments concern whether:
- reservoir operation could alter the timing of downstream releases;
- storage would affect compliance during deficit periods;
- the project’s hydrology is consistent with the award;
- environmental impacts are acceptable;
- and CWMA can reliably monitor and enforce releases after another major upstream storage structure is created.
The project should not be reported as approved merely because a revised DPR is invited. A DPR must still undergo technical, environmental, financial and statutory appraisal.
Mullaperiyar is about storage and dam operations
The Mullaperiyar commitment is legally different from Cauvery sharing.
Supreme Court judgments in 2006 and 2014 permitted Tamil Nadu to raise the reservoir level to 142 ft. The 2014 judgment also allowed balance-strengthening works intended to enable restoration of the 152-ft full reservoir level and constituted a supervisory mechanism for the dam.
The present recognised operating position is therefore:
- 142 ft permitted;
- 152 ft pursued after specified strengthening work.
The Budget’s statement that Tamil Nadu will pursue a higher level should not be interpreted as an immediate order authorising operation at 152 ft.
The principal delivery questions are:
- Which balance-strengthening works remain?
- What access or permissions are required from Kerala?
- What does the latest dam-safety evaluation require?
- Which works have been approved by the supervisory and safety authorities?
- What is the schedule for completing them?
Tamil Nadu’s own policy note says access, forest-road repair and permissions for several works have remained points of disagreement. It also records that all Mullaperiyar-related proceedings were being brought together before the Supreme Court.
The State needs a public engineering ledger, not only a legal declaration.
Anaimalaiyar carries a specific 2.5-TMC provision
The Anaimalaiyar proposal arises from the Parambikulam–Aliyar Project framework between Tamil Nadu and Kerala.
Tamil Nadu’s WRD policy note says the original agreement contains provision to divert 2.5 TMC ft from Anaimalaiyar to Tamil Nadu. Kerala has not given final consent, citing the status of its Idamalayar project. Tamil Nadu’s position is that a supplementary agreement would be sufficient. Kerala had indicated willingness to consider a weir across Italiar, a tributary of Anaimalaiyar, but final agreement has not been reported.
This is not a dispute over an undefined political promise.
It is a defined but unimplemented provision whose execution depends on:
- final alignment and engineering;
- supplementary legal terms;
- Kerala’s consent;
- measurement arrangements;
- environmental approval;
- and an implementation schedule.
The Budget should set out the next bilateral milestone rather than simply stating that the project will be pursued.
Nirar–Nallar is a larger technical negotiation
The Nirar–Nallar Multipurpose Straight Cut Scheme proposes a reservoir of approximately 7 TMC ft and a tunnel linking Upper Nirar more directly with Nallar.
Tamil Nadu argues that this would reduce conveyance losses compared with the present circuitous route through Sholayar, Parambikulam and the contour canal. Kerala has linked negotiations to its request for an increased share at Manacadavu Weir. Technical information has been exchanged, but no final interstate settlement has been published.
This project therefore requires a negotiated package, not only civil engineering.
A transparent agreement would need to state:
- water available for diversion;
- Kerala and Tamil Nadu shares;
- reservoir operations;
- hydropower arrangements;
- downstream environmental flows;
- construction and maintenance responsibility;
- and a joint measurement mechanism.
Godavari–Cauvery is not yet an assured supply
The government’s commitment to expedite the Godavari–Cauvery link is strategically attractive because it offers the possibility of transferring water towards deficit regions in southern India.
The current official position is much earlier than construction.
A draft DPR for transfer of approximately 4,189 million cubic metres—about 148 TMC ft—was circulated to participating States in January 2024. A draft Memorandum of Agreement followed in April 2024. Official parliamentary material says that building consensus among the affected States and signing the agreement remain the principal objectives.
The Union government’s own interlinking status report identifies Ken–Betwa as the only priority river-link project that has entered implementation. Godavari–Cauvery remains in the DPR, system-study and interstate-consensus stage.
Tamil Nadu may strongly support the project, but it does not yet possess an enforceable allocation from it.
Before implementation, the project requires:
- agreement on the dependable surplus available in the Godavari;
- shares for participating States and Puducherry;
- final canal termination and alignment;
- pumping and energy requirements;
- environmental and social assessment;
- land acquisition;
- financing;
- and a binding implementation MoA.
“Expedite” therefore means diplomatic and technical closure before it means construction.
River linking must be tested against energy and climate assumptions
Moving water across long distances and basin divides can require substantial pumping.
The Godavari–Cauvery project must publish:
- annual transferable quantity under normal and drought conditions;
- elevation and pumping requirements;
- electricity consumed per unit of water delivered;
- evaporation and conveyance loss;
- climate-adjusted hydrology;
- irrigation benefit;
- urban and industrial allocation;
- and the resulting cost per kilolitre.
A nominal transfer volume is not the same as dependable water at the final command area.
If the source basin faces lower future availability or participating States seek larger shares, the quantity reaching Tamil Nadu may differ materially from headline estimates.
Water quality is part of Tamil Nadu’s interstate interest
The Budget also raises pollution in the Cauvery, Vaigai and Thamirabarani and allocates ₹25 crore for feasibility studies and DPRs.
This should not be treated as unrelated environmental spending.
A river-water entitlement is meaningful only when the water remains usable.
Tamil Nadu’s WRD records say a Central Pollution Control Board report confirmed sewage-related pollution entering the Cauvery and Pennaiyar from Karnataka, while Tamil Nadu and Central agencies monitor quality near the interstate boundary.
TNPCB already maintains water-quality monitoring and approved action plans for polluted stretches, including the Cauvery and Thamirabarani, while also monitoring the Vaigai and other major rivers.
The new ₹25-crore exercise should therefore begin with a reconciliation of existing studies and action plans.
For every river reach, the State should publish:
- sewage outfalls;
- industrial discharge points;
- treatment capacity;
- actual sewage reaching treatment plants;
- compliance results;
- solid-waste accumulation;
- water-quality baseline;
- responsible local body or industry;
- and the cost and deadline for eliminating each discharge.
Riverfront development must follow pollution control
The Budget includes riverfront development among possible interventions.
Public access, parks and recreation can improve urban relationships with rivers. They should not become substitutes for water-quality restoration.
The correct sequence is:
sewage interception → industrial compliance → solid-waste control → ecological restoration → flood protection → safe public access.
Constructing promenades before eliminating sewage risks producing visually improved but ecologically failed river corridors.
Riverfront projects must also preserve:
- floodplain storage;
- natural river width;
- riparian vegetation;
- public access;
- and the rights of communities affected by land or clearance operations.
Rights enforcement must be matched by internal water management
Tamil Nadu is justified in enforcing legal allocations and opposing upstream actions it believes may impair them.
Interstate advocacy cannot replace water management within Tamil Nadu.
The State must simultaneously improve:
- reservoir and tank restoration;
- canal efficiency;
- groundwater recharge;
- irrigation scheduling;
- crop-water productivity;
- urban leakage control;
- treated-water reuse;
- and wetland protection.
The WRD’s own data show 392 groundwater assessment units classified as over-exploited in the 2024 assessment.
Interstate water is therefore one part of the security system, not a substitute for managing demand and local sources.
What Tamil Nadu should publish
The Budget commitment needs a consolidated Interstate River Rights and Delivery Dashboard.
Cauvery
- monthly quantity due;
- actual Billigundlu flow;
- reservoir storage;
- CWRC and CWMA direction;
- cumulative surplus or shortfall;
- corrective release ordered;
- delta irrigation status.
Mekedatu
- revised DPR status;
- CWC appraisal stage;
- court proceedings;
- environmental appraisal;
- Tamil Nadu submissions;
- effect on award compliance.
Mullaperiyar
- recognised operating level;
- strengthening works completed and pending;
- Kerala permissions required;
- dam-safety inspections;
- supervisory directions;
- path to any future level increase.
Anaimalaiyar and Nirar–Nallar
- interstate meeting dates;
- technical issues;
- water-sharing terms;
- supplementary agreement status;
- DPR and clearance stage.
Godavari–Cauvery
- draft DPR status;
- State comments;
- draft MoA;
- States that have agreed;
- hydrological quantity;
- environmental studies;
- financing and implementation decision.
River pollution
- outfalls mapped;
- treatment works;
- industrial compliance;
- water-quality results;
- project expenditure;
- reach-wise restoration progress.
The public-interest test
The Budget correctly recognises that interstate river water is central to Tamil Nadu’s agriculture and long-term water security.
Its commitments must now be separated into legally accurate categories.
Cauvery releases can be demanded through an existing adjudicated framework.
Mullaperiyar requires dam strengthening and operational compliance.
Anaimalaiyar and Nallar require an interstate agreement with Kerala.
Godavari–Cauvery requires consensus before implementation.
River pollution requires service and enforcement projects—not another collection of unconnected studies.
Tamil Nadu’s water position will be strongest when every legal claim is paired with real-time flow data, every negotiated project has a dated milestone and every received unit of water is protected from pollution and distribution loss.
