Sewage treatment plants in Mallorca
Septic tank, treatment plant or holding tank, the documents and maintenance, in detail.
See the guide →Treatment plants · Petra
Sewage treatment plants in Petra, above an aquifer with too many nitrates
In Petra the mains sewer reaches the village, but 432 of its 3,265 residents live in country houses (INE, Nomenclátor 2025), and there each house treats its own waste water. Underneath lies the groundwater body that the Water Plan lists in poor status because of nitrates. We are Joaquín and Juan, installers in Mallorca since 1998: we supply the new treatment plant, install it, do the electrics and prepare and sign the documents for your architect or engineer to file.
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- New approved unit
- Signed documents
- Vulnerable zone checked
- Since 1998
GRAF one2clean · Image: GRAF
Your area
The water under Petra, according to the Water Plan
Annex 9 of the Balearic Water Plan has an entry bearing the village's name: the Petra groundwater body (1815M4), which covers 155 km² of the Pla.
Nitrates: 98 mg/l
The Petra body is in poor chemical status because of nitrates: 98 mg/l on average, almost double the 50 mg/l that mark good status. It has improved —in the previous cycle it was 118 and between 2000 and 2012, 214— but not enough. The Balearic Government's Decree 18/2023 declares 46.4 km² of the municipality of Petra a nitrate-vulnerable zone.
An aquifer at its limit
Its abstraction index is 99%, and the Plan asks for abstraction to be cut by 20%. Irrigating the garden with the house's treated water, as the rules require, is water that does not come out of the well.
What has already been done with the village's treatment works
The public treatment works shared by Sineu, Petra, Maria de la Salut and Ariany is scheduled for remodelling, and irrigation with reclaimed water in Maria, Petra and Ariany appears in the Plan as a measure already carried out. In a country house, the rules ask for the same on a small scale: treat properly and reuse on the plot.
Sources: Balearic Water Plan, Royal Decree 49/2023 (regulations, art. 70, 71, 76 and 77) · Annex 9 of the Plan, entries for the groundwater body “Petra (1815M4)” and the body “Ariany (1816M1)” · EN 12566 · manufacturer's manual (GRAF one2clean, as an example).
The rules here
What the rules require of a country house in Petra
Every house with no access to the network needs an on-site treatment system, a sealed holding tank or a natural system with a favourable report (art. 70.1 of the Water Plan, Royal Decree 49/2023). The treated water is reused on the plot itself, with 25 m² of green area per population equivalent (art. 70.12), and in a home one is counted per bed space (art. 70.8).
If the plot falls in a high-vulnerability zone of the aquifer or inside the perimeter of a public supply well, the treatment plant also includes denitrification and disinfection (art. 70.10, table 13). We check it on the map of the Balearic Directorate-General for Water Resources before giving you a price.
What we do
What we do in Petra, and what others do
- A new treatment plant suited to the aquifer under Petra: approved with CE marking and EN 12566 (art. 70.14) and, if your plot shows high vulnerability or lies in the protection zone of a supply well, with denitrification and disinfection (art. 70.10). We work with all brands; for example, the GRAF one2clean.
- Installation, electrics and commissioning at your country house, as an authorised low-voltage installation company, with the outlet of the treated water taken to the garden area of the finca. We don't subcontract anyone.
- The documents for the responsible declaration to the DGRH (art. 70.4): purchase and installation, specifications, performance and maintenance plan, prepared and signed by us as the installation company. Your architect or engineer files them.
- Your builder digs the pit, following our written instructions based on the manufacturer's and bearing in mind where your well and your neighbours' wells are (art. 70.7). The sludge is removed by an authorised waste company; the receipts are kept for five years (art. 70.7.f).
- The services: those required by the rules or, if the manufacturer asks for more, the manufacturer's (on the GRAF one2clean, twice a year), with a signed report and the maintenance plan written down for the owner of the finca.
How we work
How we do it in Petra, in 3 steps
1
We check your plot over the Petra water body
With the location, the bed spaces and a few photos, we check on the DGRH map how vulnerable the aquifer is, here at 98 mg/l of nitrates, and whether there are supply wells nearby.
2
The right unit and a written quote
Depending on what the map shows, with or without denitrification, we put the unit, installation, electrics and documents in writing. Your builder gets how the pit must be.
3
We install, irrigate and sign
We install once the pit is ready, start the blower, leave the treated water running to the garden area and hand you the signed folder for your engineer.
Keep learning
More on treatment plants and energy in Petra
The general guide to treatment plants and what else we do in your area.
Solar panels in Petra
Self-consumption for the house, the treatment plant blower included.
See solar in Petra →Heat pumps in Petra
Heating and hot water with a heat pump.
See heat pumps in Petra →Across Mallorca
Sewage treatment plants in the Pla de Mallorca: Sineu · Llubí · Algaida · Porreres, or see the guide to sewage treatment plants in Mallorca →
Need the house drainage (downpipes, rainwater, chambers)? Drainage in Mallorca →
Sewage treatment plants near Petra: Santa Margalida · Manacor
Also in Petra: air conditioning
See our work and customer reviews on the JSL Google Maps profile →
Common questions
Frequently asked questions about treatment plants in Petra
Why does the treatment plant matter so much in a country house in Petra?
Because the aquifer underneath, the Petra body (1815M4), is in poor status because of nitrates: 98 mg/l on average according to Annex 9 of the Balearic Water Plan, when good status stops at 50. A septic tank that only settles adds nitrogen to the ground; a treatment plant with the performance required by art. 70.10 of the Plan, with the water reused on a green area, does not.
Is my finca in Petra in a nitrate-vulnerable zone?
Probably: the Balearic Government's Decree 18/2023 (BOIB no. 39 of 28-3-2023) declares 46.4 km² of the municipality of Petra, which has about 70, a vulnerable zone. That declaration mainly regulates agricultural fertilising. For your treatment plant what counts is the vulnerability of the aquifer on your plot: if it is high, denitrification and disinfection are needed (art. 70.10 of the Water Plan). We check it on the DGRH map.
Can I water the fruit trees with the treated water?
The general rule is to reuse it on your plot, on a green area: 25 m² per population equivalent (art. 70.12 of the Balearic Water Plan, Royal Decree 49/2023). In Petra, with the aquifer abstracted at 99%, it is irrigation that does not come out of the well. How that irrigation is distributed and over which planting we define with the manufacturer of the unit and with your architect or engineer.
Which documents have to be filed, and who files them?
A responsible declaration to the Balearic Directorate-General for Water Resources, with proof of purchase and installation, the technical specifications, the performance and the maintenance plan (art. 70.4 of the Balearic Water Plan). We prepare and sign that documentation as the installation company, and your architect or engineer files it.
I have a well on the finca: how far away does the treatment plant go?
The Plan requires the system to be sited without polluting the groundwater and taking account of the ground and its position (art. 70.7 of the Balearic Water Plan, Royal Decree 49/2023). That's why we ask you where your well is, where the neighbours' are and whether there is a public supply well nearby: in Petra the aquifer's water already carries 98 mg/l of nitrates.
How often is the treatment plant serviced and emptied?
The services, those required by the rules or, if the manufacturer asks for more, the manufacturer's: on the GRAF one2clean, for example, twice a year. The sludge is emptied by an authorised waste company at the manufacturer's interval, and the receipts are kept for five years (art. 70.7.f of the Balearic Water Plan). In a country house in Petra we leave it in writing for the owner in the maintenance plan.
Quality
We work with all brands
As an example, GRAF tanks. We propose the unit for each house and what the area requires.
A country house in Petra with no mains sewer?
Send us the location, the bed spaces of the house, where the water will go and a few photos. We reply within 24-48 hours on working days.