ISKI's 2026 Push: An 8 Billion Lira New Wastewater Program
A Major Transformation in Istanbul's Wastewater Infrastructure
The Istanbul Water and Sewerage Authority (ISKI) has unveiled its investment program covering 2026 through 2028. With a budget exceeding 8 billion lira, the plan targets shifting wastewater that is still discharged to the sea after only preliminary treatment to advanced biological treatment. The program is being described as the most comprehensive wastewater investment plan in the past decade.
Which Plants Are Being Renewed?
Six main projects stand out in ISKI's investment list:
- Atakoy Advanced Biological Treatment Plant capacity expansion: 600,000 m³/day
- Baltalimani plant: transition from preliminary to advanced biological treatment
- Comprehensive renewal of the Yenikapi plant
- Three new package treatment plants on the Anatolian side
- Expansion of the Umraniye-Cekmekoy line
- 320 km of additional sewer network
Total additional treatment capacity reaches 1.4 million m³/day. This figure will increase Istanbul's existing advanced treatment capacity by approximately one third.
Aligned with the Sea of Marmara Action Plan
Discharge criteria have been notably tightened under the Sea of Marmara Action Plan launched after the 2021 mucilage crisis:
- Total nitrogen discharge limit: 10 mg/L (previously 15 mg/L)
- Total phosphorus: 1 mg/L
- Suspended solids: 30 mg/L
- Advanced treatment mandatory at all plants discharging to the Marmara by end of 2028
These criteria apply to both municipal and industrial-source plants. The program also introduces 24-hour real-time online monitoring as a requirement.
Financing Model
The project uses a mixed financing model:
- ISKI own resources: 40 percent
- World Bank loan: 2.1 billion lira equivalent
- Iller Bankasi loan: 1.8 billion lira
- EU IPA funds: 600 million lira
- Green bond issuance option: under evaluation
The green bond option stands out as a new financing instrument for public infrastructure investments in Turkey.
Employment and Domestic Production
The project mandates a minimum 65 percent domestic equipment usage rate. This threshold opens a significant demand window for Turkish treatment equipment manufacturers. Domestic supplier shares are expected to rise notably across pumps, blowers, decanter centrifuges, UV disinfection and instrumentation segments. The construction phase is projected to create about 4,500 direct jobs, with 1,200 qualified personnel needed during operations.
Timeline
Tenders are planned to be completed in 2026, construction to start in the last quarter of 2026, and plants to be commissioned in stages by end of 2028. With program completion, nearly 100 percent of Istanbul's wastewater is expected to pass through advanced biological treatment.
What This Means for Turkey
ISKI's move serves as a defining reference point not just for Istanbul but for the entire country. Similar criteria are expected to be implemented in other major cities and industrially dense regions. Sector-wide demand for advanced treatment technologies, online monitoring systems and energy recovery projects will rise significantly over the next three years. For engineering, consulting and equipment supply companies, this period represents an important growth window.