The sewage treatment plants of the Balearic Islands, at the limit due to population increase and tourist overcrowding

PalmaThe sewage treatment plants in the Balearic Islands are increasingly under pressure due to population growth and tourism activity. This is the main warning in the annual report by the Balearic Islands Water Observatory, prepared by the Water Alliance based on data from the 80 treatment plants managed directly by the Balearic Agency for Water and Environmental Quality (Abaqua).

In 2025, these facilities treated 49.3 cubic hectometers of wastewater. The volume has increased by 15.1% in Mallorca, 10.1% in Menorca, and 6.8% in Ibiza over five years, while in Formentera it has decreased by 19%. The increase is particularly notable on the coast, where the treated flow has grown by 30.3%, compared to 0.8% in inland centers. In Cales de Mallorca, for example, it has almost tripled.

In Mallorca, Campanet, Campos, Consell, and Inca exceeded their design flow during most of 2025. Campanet did so for all twelve months, despite having received 18.6% less wastewater than in 2021. The Alliance considers that this proves the infrastructure's capacity was already insufficient.

The problem is not just one of capacity. The quality of the water reaching the treatment plants is also worsening. In Mallorca, 38 of the 56 facilities recorded at least one month of non-compliance in influent quality, while 27.6% of the flow arrived with some form of non-compliance, compared to 15.1% in 2021. The situation worsens during the summer months, when the treated flow increases.

Another prominent problem is salinity. 76.2% of the influent volume in Mallorca exceeded the threshold in 2025. According to the Alliance, seawater infiltrations into the sewage networks hinder the treatment process and can prevent the subsequent reuse of the water. In Ibiza, this indicator reaches 97.9%, the highest value in the report.

Ibiza improves with the new La Coma treatment plant

Ibiza shows a more moderate growth in the volume of wastewater, but it is the island with the worst input quality: the 11 treatment plants recorded at least one month of non-compliance, and 40.1% of the annual flow arrived with problems. On the other hand, the new La Coma treatment plant, which already treats 46.9% of the island's flow, has allowed output compliance to rise to 88.8%.

Menorca has recorded a 10.1% increase in the volume of wastewater. Ferreries is one of the most concerning cases, having exceeded its design flow for eight months in 2025, despite having been remodeled in 2017. The island, however, maintains the best compliance levels in the Balearic Islands, with 98.4% of the flow within annual limits.

Formentera is the only island where the volume of wastewater is decreasing and also the only one without any output non-compliance for five consecutive years. Nevertheless, its only treatment plant is over 25 years old and is awaiting a renovation budgeted at 6.1 million euros.

An aging fleet of treatment plants

The Alliance warns that the main problem is also the age of the infrastructure. 82.5% of the 80 wastewater treatment plants managed by Abaqua were built before the year 2000 and half have never been remodeled. Between 2018 and June 2026, only six remodeling works of more than one million euros have been put out to tender.

The entity demands that any new urban growth be conditioned on the real capacity of the sanitation infrastructure and that the actions foreseen in the Hydrological Plan be accelerated. It also requests that sewage networks be repaired to reduce seawater infiltration and to promote the reuse of treated water.

"Wastewater treatment plants are silently absorbing the pressure of population growth and tourist overcrowding that does not stop," warned the spokesperson for the Water Alliance, Rafael Tur, who calls for a modernization of administrative procedures to accelerate works that, according to the entity, can now take decades.