Sewage treatment plants in Cala d'Or, for year-round and holiday villas

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Cala d'Or: what to check before choosing the unit

Three public facts that change the treatment plant of a house in Cala d'Or.

Two town halls

The centre of Cala d'Or belongs to Santanyí, but Cala Ferrera and Cala Serena are in the municipality of Felanitx. For a new build on urban land with no mains sewer, the licence comes from the relevant town hall, which asks for proof of the prior notice given to the Balearic water authority, Recursos Hídrics (fourth transitional provision of the Balearic Urban Planning Act, Law 12/2017); from that notice there are two years at most for the responsible declaration to the DGRH (art. 70.5 of the Balearic Islands Water Plan, RD 49/2023).

The Prat de Porto Petro

Between Cala d'Or and Portopetro, the Water Plan's wetland catalogue lists the Prat de Porto Petro (code MAZH18). A villa with 12 population equivalents or more within 500 m needs prior authorisation, not just the responsible declaration. In that authorisation silence means no: if the DGRH does not answer, the answer is no.

How vulnerable the aquifer is

On the government's aquifer vulnerability map (IDEIB viewer), around Cala d'Or there are high-vulnerability zones next to moderate ones. In high vulnerability, the Water Plan only allows discharge to garden and also lists denitrification and disinfection, recommended up to 12 population equivalents and required above 12 (art. 70.10, tables 13 and 14). It is the first thing we check with the plot's location, because it decides the unit.

The paperwork

Villas that close for the winter

If the house stands empty for weeks or months, the blower has to keep running: if the power is switched off when you leave, the bacteria die and on your return the plant does not treat. For that use, on a GRAF one2clean for example, the carbon-dosing module (Pack +C) is added, which feeds the biology while nobody is there. And we size the unit for the most people in August, not the yearly average; as a guideline equivalence, the Plan gives 1 population equivalent per bed (art. 70.8).

Where treatment is not viable because the use is very seasonal, the rules allow a holding tank (art. 70.2): it discharges nothing, but it has to be emptied completely each time it fills, by an authorised waste management company. If there is a garden, a treatment plant almost always works out better, and the water irrigates: 25 m² of garden per population equivalent (art. 70.12).

Sources: Balearic Islands Water Plan, RD 49/2023 (art. 70, 76 and 77) · wetland catalogue, supply boreholes and aquifer vulnerability in the Balearic government IDEIB viewer · nitrate vulnerable zones (Decree 18/2023).