Almost 98% of the wastewater entering Ibiza's wastewater treatment plants exceeded the applicable salinity threshold in 2025, according to a new analysis by the Aliança per l'Aigua based on data from the Balearic Water and Environmental Quality Agency, ABAQUA.

The figure, 97.9%, is the highest recorded among the four Balearic Islands analysed and has not improved over the previous five years, according to the organisation's 2025 Water Observatory report.

The report identifies seawater infiltration into municipal sewer networks as the main cause of the high salinity. This creates a major problem for wastewater treatment and makes the treated water unsuitable for certain forms of reuse, including agricultural irrigation and aquifer recharge.

At the same time, the report contains an important positive development for Ibiza: the quality of treated water leaving the island's plants has improved substantially following the opening of the new Sa Coma wastewater treatment plant.

The findings nevertheless indicate that Ibiza's wastewater infrastructure remains under significant pressure, particularly during the summer tourism season.

Almost 98% of Ibiza's wastewater input is affected by salinity

The most striking figure in the report is the 97.9% salinity rate.

According to the Aliança per l'Aigua, 97.9% of the wastewater entering Ibiza's treatment plants exceeded the established salinity threshold during 2025.

The organisation says the figure is the highest in its analysis of the Balearic Islands and has shown no improvement over the last five years.

Several individual plants recorded an even higher figure. The treatment plants serving Vila, Sant Antoni and Can Bossa reached 100% of their annual wastewater input exceeding the salinity threshold.

The report attributes the problem to seawater entering municipal sewer networks, meaning the treatment plants receive wastewater that already contains an unusually high concentration of salt before the treatment process begins.

Why is seawater entering the sewage network?

The Aliança per l'Aigua says the high salinity is a consequence of seawater infiltrating the municipal sewerage system.

This can occur when seawater enters underground sewer infrastructure through leaks, damaged pipes, joints or other points where the system is not sufficiently watertight.

For wastewater treatment plants, this creates a problem before treatment even begins.

The water arriving at the plant contains substantially more salt than normal domestic wastewater, making the treatment process more difficult and limiting the potential uses of the resulting treated water.

The organisation is therefore calling for municipal sewerage networks to be repaired so that seawater infiltration can be reduced at source.

High salinity limits water reuse

One of the most important consequences identified in the report is the effect on water reuse.

The Aliança per l'Aigua says the salinity of Ibiza's wastewater makes it impossible to reuse the treated water for agricultural irrigation or aquifer recharge.

This is particularly significant on an island where water resources are limited and where authorities have increasingly promoted desalinated water, groundwater management and the reuse of treated wastewater as part of broader water planning.

The potential to reuse wastewater is reduced when the water entering treatment plants already contains excessive amounts of salt.

The problem therefore affects not only wastewater disposal but also Ibiza's wider efforts to make better use of every available water resource.

The new Sa Coma plant has significantly improved treatment results

Despite the problems with incoming wastewater, the report records a substantial improvement in the quality of treated water leaving Ibiza's plants.

Overall compliance based on the relevant concentration thresholds increased to 88.8%, compared with much lower levels before the Sa Coma facility became operational.

The new Sa Coma wastewater treatment plant is now responsible for treating 46.9% of Ibiza's total wastewater flow.

According to the Aliança per l'Aigua, Sa Coma achieves 100% compliance with the applicable criteria.

Its contribution has therefore made a significant difference to Ibiza's overall treatment results.

The improvement does not solve the underlying wastewater problem

The improved performance of Sa Coma does not mean that Ibiza's entire wastewater system is operating without problems.

The report makes a distinction between the quality of water entering the plants and the quality of water leaving them.

The new facility has substantially improved the latter, but the former remains problematic.

All 11 Ibiza wastewater treatment plants included in the analysis recorded at least one month in 2025 in which incoming wastewater did not meet the relevant quality requirements.

Across the island, 40.1% of the total wastewater flow was associated with months in which the incoming water failed to comply.

That was the highest proportion recorded among the four islands.

Ibiza treated 6.8% more wastewater than in 2021

The quantity of wastewater being received by Ibiza's treatment plants also increased between 2021 and 2025.

The total volume rose by 6.8% during the five-year period.

This was the smallest increase among the three main Balearic islands in the report. Mallorca recorded an increase of 15.1%, while Menorca rose by 10.1%.

The Ibiza figure nevertheless represents a continued increase in the amount of wastewater that the island's treatment infrastructure has to process.

The increase was particularly pronounced in certain coastal areas.

Cala Llonga recorded an 80% increase in wastewater volume between 2021 and 2025.

Coastal areas are seeing the strongest growth

The report identifies a wider pattern across the Balearic Islands.

Wastewater treatment volumes at coastal plants increased by 30.3% between 2021 and 2025, compared with only 0.8% growth in inland areas.

The Aliança per l'Aigua links this difference to the demographic and tourism pressure concentrated in coastal areas.

For Ibiza, where much of the population growth and tourism activity is concentrated around coastal settlements, the findings highlight the particular importance of maintaining adequate wastewater infrastructure near the areas experiencing the strongest seasonal demand.

Summer creates another major pressure point

The wastewater situation becomes significantly more difficult during the summer.

The report says the volume of wastewater treated in Ibiza almost doubles during the high-season period, increasing by 99.1% compared with winter.

This means that treatment plants are dealing with dramatically higher flows precisely when tourism activity reaches its peak.

Although the report says none of Ibiza's plants exceeded their formal design flow during this period, the quality of the resulting treated water deteriorated.

The island's overall compliance based on concentration thresholds fell from 91.6% outside the summer months to 84.3% between June and September.

Eight Ibiza plants exceeded contamination thresholds during summer

Eight of Ibiza's 11 wastewater treatment plants recorded summer months in which treated water exceeded the permitted concentration threshold for biochemical oxygen demand, known as BOD5.

The affected plants were:

Cala Llonga

Sant Joan de Labritja

Port de Sant Miquel

Cala Sant Vicent

Cala Tarida

Sant Josep

Sant Antoni

Santa Eulària des Riu

The report also found that the same eight plants exceeded the applicable chemical oxygen demand, or COD, threshold during at least one summer month.

Cala Llonga recorded the highest COD level

Among the most notable results was the figure recorded at Cala Llonga.

The plant reached 870 milligrams per litre of COD during one summer measurement.

The relevant limit is 125 milligrams per litre.

That means the recorded concentration was almost seven times the established threshold.

Other significant maximum COD readings included 671 milligrams per litre at Sant Joan de Labritja, 435 at Cala Sant Vicent, 405 at Port de Sant Miquel and 370 at Cala Tarida.

Sant Josep recorded 300 milligrams per litre, Sant Antoni 210 and Santa Eulària des Riu 195.

These measurements demonstrate how sharply treated-water quality can deteriorate at some plants during periods of peak demand.

High contamination in the incoming water is a major factor

The Aliança per l'Aigua argues that the problem is not simply that the treatment plants are failing to operate correctly.

Instead, the report points to the exceptionally high contamination load of the wastewater arriving at some facilities.

This distinction is particularly important in Ibiza's case.

The island achieves a 98% compliance rate when measured according to its ability to reduce the contaminant load through treatment.

However, net compliance based on the final concentration threshold is lower, at 88.8%.

The difference suggests that some plants are achieving strong reductions from exceptionally polluted incoming wastewater but are still unable to bring every parameter below the final concentration limit.

The report identifies Cala Tarida and Can Bossa as particular concerns

The quality of wastewater entering Ibiza's plants is particularly problematic at several facilities.

Cala Tarida recorded non-compliant incoming water for 97.2% of its annual wastewater volume.

Can Bossa followed at 95.9%.

Sant Antoni recorded 60.6%, Vila 51.6%, Cala Llonga 40.8% and Sant Josep 33.9%.

These figures show that the problem is particularly concentrated at certain treatment plants rather than being evenly distributed across the island.

Sa Coma is changing Ibiza's overall picture

The new Sa Coma plant represents one of the biggest improvements highlighted in the report.

The facility now handles almost half of Ibiza's total wastewater volume.

Its 100% compliance performance has helped raise the overall island figure considerably.

The plant replaced the older Vila treatment facility and represents a major investment in Ibiza's wastewater infrastructure.

The Aliança per l'Aigua nevertheless notes that the project took many years to come to fruition, with the works being put out to tender in 2015 and completed in 2024.

Can Bossa was the only Ibiza plant to exceed design capacity

Despite the island's wastewater pressures, the report does not describe widespread formal capacity failures across Ibiza.

Only Can Bossa exceeded its design wastewater flow, and it did so during one month of 2025.

This is an important distinction from some areas of Mallorca and Menorca, where several treatment plants were operating above their design capacity for much longer periods.

For Ibiza, the principal problem identified by the report is therefore not simply insufficient plant capacity.

The quality of the incoming wastewater, particularly its salinity and contaminant load, is one of the most serious concerns.

Ibiza's wastewater volume is strongly linked to tourism

The seasonal pattern is particularly clear in Ibiza.

The volume of wastewater treated almost doubles during the summer compared with winter.

This corresponds with the island's sharp increase in population during the tourism season.

The report describes the wider pressure on Balearic treatment infrastructure as a consequence of both population growth and tourism intensity.

Between 2016 and 2025, resident populations in Mallorca, Menorca and Ibiza increased by between 12% and 16%, while the Human Pressure Index, which combines residents and visitors, increased by between 7% and 9%.

The Aliança per l'Aigua says these trends help explain the increasing pressure on water and wastewater infrastructure.

The environmental consequences extend beyond the treatment plants

The wastewater issue ultimately reaches Ibiza's coastline because treated wastewater is discharged after processing.

When plants receive exceptionally contaminated wastewater and the final treatment does not always bring every parameter below the relevant concentration threshold, there is a potential impact on the marine environment.

The report identifies several coastal treatment plants where summer discharge concentrations exceeded the applicable thresholds.

However, it is important to distinguish between a recorded failure to meet a particular wastewater concentration limit and a proven specific ecological impact at a particular coastal location.

The report establishes the wastewater quality measurements. It does not by itself establish the extent of environmental damage caused by every individual discharge.

The headline 98% figure needs context

The statement that 98% of wastewater entering Ibiza's plants is "salty" can easily be misunderstood.

The 97.9% figure refers specifically to the proportion of the volume of incoming wastewater that exceeded the salinity threshold used in the report.

It does not mean that 97.9% of the wastewater is seawater.

Nor does it mean that the entire volume consists almost entirely of seawater.

The report attributes the excessive salinity to seawater infiltration into municipal sewer networks.

This distinction is important when describing the data accurately.

The same report highlights Formentera's contrasting results

Formentera provides a very different picture.

Its wastewater volume declined by 19% between 2021 and 2025, although the report warns that missing data for part of 2024 and early 2025 means the actual reduction may be somewhat different.

Formentera's single wastewater treatment plant did not exceed its design capacity in 2025.

Most significantly, the plant achieved 100% compliance for treated water output for the fifth consecutive year.

The report found no anomalous discharge from the facility during the year.

Formentera's wastewater system is older but performs well

The strong results from Formentera come despite the age of its infrastructure.

The island's wastewater treatment plant is more than 25 years old and is currently undergoing a renovation project valued at approximately €6.1 million.

The report says that the plant has never been undersized in terms of capacity.

Its incoming wastewater quality is nevertheless less positive, with 33.3% of its annual volume associated with months of non-compliance.

Salinity also remains an issue, although it has improved significantly compared with the previous year.

In 2025, 52.8% of Formentera's incoming wastewater exceeded the salinity threshold, compared with 100% in 2024.

The wider Balearic problem

Ibiza's situation forms part of a broader problem affecting wastewater treatment infrastructure across the Balearic Islands.

The report found that wastewater volume at coastal plants across the islands increased by 30.3% between 2021 and 2025.

At the same time, 82.5% of the wastewater treatment plants included in the analysis were built before 2000.

The Aliança per l'Aigua is therefore calling for an urgent programme to modernise wastewater infrastructure across the islands.

It is also demanding action to repair municipal sewer systems and reduce seawater infiltration.

What the Aliança per l'Aigua is calling for

The organisation says several measures are necessary to address the problems identified in the report.

One of its main demands is an urgent programme to modernise ageing wastewater treatment infrastructure.

It also wants municipalities to repair sewer networks so seawater cannot continue entering the system.

The organisation further argues that new urban development should take into account the actual treatment capacity available in each municipality.

The objective is to ensure that additional development does not place further pressure on infrastructure that is already struggling during peak periods.

The report does not say every Ibiza plant is overloaded

One important finding can easily be lost among the more dramatic statistics.

The data do not show that all 11 Ibiza wastewater plants are operating beyond their design capacity.

Only Can Bossa exceeded its design capacity, and only for one month during 2025.

The bigger structural concern is therefore the quality of the wastewater entering the plants and the deterioration in treated-water quality during periods of maximum tourism pressure.

This makes infrastructure beyond the treatment plants themselves, especially municipal sewer networks, an important part of the issue.

Why this matters for Ibiza's water strategy

Ibiza faces a difficult contradiction.

The island has limited freshwater resources and is increasingly interested in reusing treated wastewater.

At the same time, a huge proportion of incoming wastewater is affected by excessive salinity.

When seawater enters the sewage network, it effectively reduces the value of a potentially reusable water resource.

The problem therefore affects the entire water cycle.

Fixing leaks and infiltration points in sewage networks could help improve treatment performance while also increasing the potential for safe reuse of treated wastewater.

Sa Coma shows that investment can make a difference

The improvement following the opening of Sa Coma is one of the most positive findings in the report.

Ibiza's overall treated-water compliance has increased substantially, and Sa Coma itself is achieving full compliance according to the report's criteria.

The facility now treats 46.9% of the island's wastewater.

Its performance demonstrates that modern infrastructure can significantly improve the treatment system's overall results.

The challenge now is extending those improvements across the rest of the island.

Ibiza's coastal treatment plants remain under pressure

The plants serving coastal communities are particularly important because they handle wastewater from areas with significant tourism activity.

Cala Llonga's 80% increase in wastewater volume between 2021 and 2025 is one example.

During summer, the overall flow across Ibiza's plants nearly doubles.

The result is a system that may remain within formal design capacity while still experiencing significant deterioration in treated-water quality.

This suggests that capacity alone is not a sufficient measure of whether wastewater infrastructure can cope with Ibiza's seasonal pressure.

A five-year warning over salinity

Perhaps the most concerning aspect of the salinity figures is that they have not improved.

The Aliança per l'Aigua says the 97.9% figure for Ibiza has remained essentially unchanged for five years.

That means the seawater-infiltration problem is not a temporary result of the 2025 tourism season.

It is a persistent infrastructure issue.

Repairing municipal sewerage systems therefore represents one of the clearest potential interventions identified by the report.

Ibiza's wastewater challenge in numbers

Wastewater volume increase, 2021-2025: 6.8%

Increase at Cala Llonga: 80%

Share of Ibiza incoming wastewater exceeding salinity threshold: 97.9%

Ibiza plants with at least one month of incoming-water non-compliance: 11 out of 11

Share of island wastewater flow associated with incoming-water non-compliance: 40.1%

Sa Coma's share of Ibiza's wastewater flow: 46.9%

Sa Coma compliance: 100%

Overall treated-water compliance by concentration threshold: 88.8%

Summer increase in wastewater flow compared with winter: 99.1%

Summer treated-water compliance by threshold: 84.3%

Highest summer COD reading: 870 mg/l at Cala Llonga

COD legal threshold: 125 mg/l

Number of Ibiza plants exceeding the summer COD threshold: 8 of 11

Ibiza plants exceeding their design capacity: Can Bossa, for one month

What needs to happen next?

The findings place significant responsibility on the island's municipalities and regional authorities.

The Aliança per l'Aigua wants municipal sewer networks repaired so seawater infiltration can be reduced.

It also wants further investment in wastewater treatment plants and greater consideration of treatment capacity before new development is approved.

At the same time, the improved performance of Sa Coma demonstrates that infrastructure investment can deliver measurable improvements.

The challenge will be ensuring that the benefits of the new plant are not undermined by poor-quality wastewater entering the wider system.

Ibiza's wastewater system faces a complicated problem

The latest Water Observatory report presents a more complicated picture than the headline figure alone suggests.

Ibiza is not simply suffering from a lack of wastewater treatment capacity.

The island has made significant progress since the opening of Sa Coma, and only one plant exceeded its design capacity during 2025.

Yet almost 98% of incoming wastewater exceeded the salinity threshold, all 11 plants experienced incoming-water quality non-compliance at some point during the year and eight plants recorded summer treated-water concentrations above the COD threshold.

The evidence points toward a combination of ageing sewer infrastructure, seawater infiltration, high contaminant loads and enormous seasonal fluctuations in wastewater flows.

For Ibiza, solving the problem will therefore require more than building new treatment plants.

It will also require fixing the networks that carry wastewater to those plants in the first place.

Key Facts

Report: 2025 Water Observatory sanitation and wastewater-treatment analysis

Published: September 4, 2026

Data source: ABAQUA

Organisation behind analysis: Aliança per l'Aigua

Ibiza wastewater increase, 2021-2025: 6.8%

Incoming wastewater exceeding salinity threshold: 97.9%

Incoming-water non-compliance: All 11 Ibiza treatment plants recorded at least one affected month

Sa Coma share of Ibiza's wastewater flow: 46.9%

Sa Coma treatment compliance: 100%

Overall Ibiza treated-water compliance by concentration threshold: 88.8%

Summer wastewater-flow increase: 99.1%

Plants exceeding summer COD threshold: 8 of 11

Highest recorded summer COD: 870 mg/l at Cala Llonga

Legal COD threshold: 125 mg/l

Plants exceeding design capacity: Can Bossa for one month

Main cause identified for high salinity: Seawater infiltration into municipal sewer networks

Main recommendations: Repair sewer networks, modernise treatment infrastructure and ensure new development is matched to real treatment capacity