Five of Israel's six main desalination plants were shut down for days in September 2026 after an exceptional algae bloom clogged their filters, leaving the country facing weeks of water shortages, according to a The Guardian report published 25 September. Scientists quoted in the report link the bloom, which stretched up to 100 km along the southern Mediterranean coast, to a massive discharge of untreated sewage from Gaza, where all five of the territory's wastewater treatment plants are out of service.
Key takeaways
- Five of Israel's six main desalination plants shut down for days after a microalgae bloom up to 100 km long clogged their filters, according to a The Guardian report published 25 September.
- All five of Gaza's wastewater treatment plants are out of service, sending an estimated 45,000 m³/day of untreated sewage into the Mediterranean, the The Guardian reports.
- Israeli bombardment has destroyed 90% of Gaza's water and sanitation infrastructure since 7 October 2023, according to a Médecins Sans Frontières report cited by the The Guardian.
- Israeli authorities have reduced water supplies in the south of the country and ordered farmers to halt irrigation while the desalination system is restored, the The Guardian reports.
What happened: the bloom and the cross-border sewage load
Desalination plants along Israel's southern Mediterranean coast feed filters with raw seawater, so any sustained rise in nutrients, biomass or organic load upstream of the intake translates directly into higher pretreatment burden, shorter filter runs and more frequent chemical cleans, the The Guardian reports. The Zalul Environmental Association, an Israeli NGO, said untreated sewage from Gaza carries nitrogen and phosphorus that feed microalgae and cyanobacteria along the coast.
“Pollution does not recognise political borders,” the Zalul Environmental Association told the The Guardian. “The discharge of untreated sewage from the Gaza Strip into the sea is contributing to the worsening crisis affecting the Israeli desalination facilities.”
Jack Gilron, a professor emeritus and desalination expert at Ben-Gurion University's Zuckerberg Institute for Water Research, told the The Guardian that the discharge “increases risks to Israel's water production infrastructure along the southern Mediterranean coast” and that the incident “reinforces the need to prepare against threats to one of Israel's main sources of drinking water.”
What happened: the Gaza side of the failure
On the Gaza side, Omar Shatat, deputy executive director of the Coastal Municipalities Water Utility, told the The Guardian that all five of the territory's wastewater treatment plants are out of service, leaving an estimated 45,000 m³/day of untreated sewage to flow into the Mediterranean. A further 15,000 m³/day seeps into the groundwater from soakaway pits, particularly in the informal camps in al-Mawasi, the same source reports.
“This is a catastrophic situation environmentally and from a public-health perspective,” Shatat told the The Guardian. Before the war, 80% of Gaza's water came from a coastal aquifer now contaminated by seawater and wastewater, and three pipelines controlled by the Israeli water authority were cut at the start of the war and have only partially reopened, the The Guardian reports.
The immediate operational response inside Israel is rationing. Authorities are urging consumers to use water “judiciously,” supplies have been reduced in the south and farmers have been instructed to halt irrigation, which the The Guardian reports economists expect to push food prices higher. Zalul and EcoPeace Middle East have asked Cogat, the Israeli agency that administers civilian affairs in Gaza, to help restore the territory's sewage system and allow wastewater to be treated in Israeli-controlled areas.
Specification read: what the numbers mean for a buyer
The reported Gaza figure is 45,000 m³/day of untreated sewage flowing to the sea, or 45 MLD, with a further 15,000 m³/day infiltrating groundwater, 15 MLD, giving a combined wastewater load of roughly 60,000 m³/day, 60 MLD, before any rainfall-driven peaking (arithmetic from figures in the The Guardian report). The reported Israeli impact is a bloom stretching up to 100 km along the southern Mediterranean coast that forced five of six main desalination plants offline for days, a sudden raw-water quality shock at the plant intake rather than a capacity loss inside the plant itself.
A plant built to treat a municipal sewage flow of this order normally runs screening, grit removal and primary clarification, followed by a biological stage (A2O, MBR, MBBR, SBR or UASB depending on footprint and effluent targets), then tertiary polishing and disinfection before reuse or discharge, with DAF or ZLD trains added where nutrient limits are tight. This event is a pretreatment and intake-protection problem: the Israeli plants were not designed for raw seawater carrying the nutrient, algae and organic load of an untreated domestic stream, so screen, DAF and UF duty collapse first. For plants on the Mediterranean, the Red Sea or any eutrophic coastal intake, the procurement read is that a high-rate integrated sewage treatment train on the inland side is the only way to keep the desalination intake within its design envelope, and the water purification pretreatment step has to be sized for bloom events, not average summer seawater. If your plant takes raw surface or seawater in the 10 to 100 MLD range with BOD or COD in the hundreds of mg/L, a coastal municipal utility, and is now under compliance pressure to maintain output through algal events, this is the operating regime you should be specifying for, not the one on the nameplate.
FAQ
What flow rate defines a municipal coastal treatment plant in this class? The reported Gaza load is 45,000 m³/day of untreated sewage to the sea plus 15,000 m³/day to groundwater, 60,000 m³/day combined, according to the The Guardian. Plants in the 10 to 100 MLD band typically use screening, primary clarification, biological treatment (A2O, MBR or MBBR), tertiary filtration and disinfection, with DAF for algae-heavy periods.
What is the lead time for a packaged MBR or MBBR unit in this size class? General industry range, not from the sources: a prefabricated 10 to 50 MLD MBR or SBR skid train is typically delivered 16 to 30 weeks after PO, with civil works adding 6 to 12 months. Containerised units can shorten delivery to 8 to 14 weeks but cap out at lower flows.
How do buyers screen suppliers for a coastal, algae-prone intake? The reported failure mode here is biological fouling of intake and pretreatment, not a hydraulic shortfall, the The Guardian reports. Shortlist on demonstrated DAF or dissolved-air flotation performance on algae-laden raw water, on UF membrane clean-in-place frequency under bloom conditions, and on reference plants with the same source water.
What is the indicative capex range per MLD for a 50 MLD municipal plant? General industry range, not from the sources: turnkey municipal plants in the 20 to 100 MLD band commonly price between roughly 0.4 and 1.2 million USD per MLD of installed capacity, with MBR trains sitting at the upper end and conventional activated sludge at the lower end, before land and outfall costs.
