Sewage treatment plants in Mallorca
Septic tank, treatment plant or holding tank, the documents and maintenance, in detail.
See the guide →Treatment plants · Sencelles
Sewage treatment plants in Sencelles, where half the population lives in the countryside
According to INE's 2025 gazetteer, 2,202 of Sencelles' 4,077 residents live scattered across the countryside, outside the villages: more than half. On rural land there is no mains sewer, and the Balearic Water Plan requires each house to have its own system. 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
- Nitrates and wells, checked
- Since 1998
Your area
Two aquifers with nitrates under Sencelles
Annex 9 of the Balearic Water Plan places the municipality of Sencelles over two groundwater bodies, Inca and Llubí. Both are in poor chemical status because of nitrates, and that is exactly what a well-chosen treatment plant helps not to make worse.
Inca, to the west
The Inca groundwater body (1811M3), of 98 km², is shared by Sencelles, Consell, Binissalem, Lloseta, Inca and Santa Eugènia. It has 66 mg/l of nitrates on average and vulnerable-zone programmes since 2010. The Plan asks for those programmes to continue and for waste-water treatment to be improved.
Llubí, to the east
The Llubí groundwater body (1811M2), of 94 km² and made of Miocene limestone and calcarenite, reaches Sencelles from Muro, Llubí, Sineu and Costitx. It carries 54 mg/l of nitrates and is at risk from chlorides (216 mg/l): the Plan asks for abstraction and the depth of well pumps to be controlled.
Fincas with their own well
Many country houses in Sencelles have a well. The treatment plant is sited taking the ground into account and without polluting the groundwater (art. 70.7.a and c): that's why we ask where your well and your neighbours' wells are before deciding where the unit and the irrigation area go.
Sources: Balearic Water Plan, Royal Decree 49/2023 (regulations, art. 70 and 71) · Annex 9 of the Plan, sheets for the groundwater bodies “Inca (1811M3)” and “Llubí (1811M2)” and general measures for rural land · EN 12566 · manufacturer's manual (GRAF one2clean, as an example).
The rules here
What changes in an area with nitrates
The treated water is reused on the plot itself, with 25 m² of green area per population equivalent (art. 70.12). If the plot lies in a high-vulnerability zone of the aquifer, the unit must also have denitrification and disinfection (art. 70.10, table 13). We check it on the map viewer of the Balearic water authority (Direcció General de Recursos Hídrics) with your location.
For Mallorca, the Water Plan provides for a measure to upgrade, replace or install septic tanks on rural land. A cesspit is none of the solutions the rules accept (art. 70.1): what we install is a new treatment plant, approved with CE marking and compliant with EN 12566 (art. 70.14).
What we do
What we do in Sencelles, and what others do
- Out with the cesspit: in its place, a new treatment plant, approved with CE marking and compliant with EN 12566 (art. 70.14). Over Inca or Llubí, in a high-vulnerability zone, it includes denitrification and disinfection. We work with all brands; as an example, the GRAF one2clean.
- Where the unit goes we decide with you, based on your well and the neighbours', without polluting the groundwater (art. 70.7.a and c). Your builder digs the pit following what we give them in writing according to the manufacturer, and an authorised waste company empties the sludge (art. 70.7.f).
- Installation, electrics and commissioning at country houses in Sencelles, Biniali, Ruberts or Jornets, as a licensed low-voltage installation company. We don't subcontract anyone.
- Servicing for the weekend house too: what the rules require or, if the manufacturer asks for more, the manufacturer's (on the GRAF one2clean, twice a year), with a signed report, and the blower kept powered even when nobody is home.
- The responsible declaration to the Direcció General de Recursos Hídrics, with purchase, installation, performance and maintenance plan (art. 70.4). We prepare and sign it as the installation company; your architect or engineer files it.
How we work
How we do it in Sencelles, in 3 steps
1
Where your well is
Send us the location, bed spaces, where the estate's well is and some photos. We see whether the plot is over Inca or Llubí and in which vulnerability zone.
2
Unit and irrigation, in the quote
We give it to you in writing: unit, installation, electrics, documents and where the green area of 25 m² per population equivalent sits in relation to the wells.
3
Installation and documents
Once your builder has opened the pit, we install and start the unit, and your engineer receives the documents, prepared and signed, to file.
Keep learning
More on treatment plants and energy in Sencelles
The general guide to treatment plants and what else we do in your area.
Solar panels in Sencelles
Self-consumption for the house, the treatment plant blower included.
See solar in Sencelles →Heat pumps in Sencelles
Heating and hot water with a heat pump.
See heat pumps in Sencelles →Across Mallorca
Sewage treatment plants in the Raiguer and the Tramuntana: Alaró · Consell · Selva · Bunyola · Esporles, or see the guide to sewage treatment plants in Mallorca →
And for the summer: air conditioning in Sencelles →
Need the house drainage (downpipes, rainwater, chambers)? Drainage in Mallorca →
Sewage treatment plants near Sencelles: Inca · Binissalem · Santa Maria del Camí · Santa Eugènia · Costitx
See our work and customer reviews on the JSL Google Maps profile →
Common questions
Frequently asked questions about treatment plants in Sencelles
Does my country house in Sencelles need a treatment plant?
If it has no access to the mains sewer, yes: the Balearic Water Plan (Royal Decree 49/2023, art. 70.1) requires an on-site treatment system, a sealed holding tank emptied periodically or a natural system with a favourable report. In Sencelles that is the case for many people: according to INE (2025 gazetteer), 2,202 of its 4,077 inhabitants live scattered across the countryside, outside the villages.
What does it mean that Sencelles lies over aquifers with nitrates?
That the groundwater is already above the good-status limit, 50 mg/l: the Inca body has 66 mg/l and the Llubí body 54 mg/l, according to Annex 9 of the Balearic Water Plan (Royal Decree 49/2023). For your treatment plant it means irrigating a green area of the plot with the treated water and, if the plot falls in a high-vulnerability zone, adding denitrification and disinfection (art. 70.10).
I have a well on the finca: how far away does the treatment plant go?
The Water Plan gives no single distance: it requires the system to be sited without polluting the groundwater and taking the ground and its position into account (art. 70.7.a and c of the Balearic Water Plan, Royal Decree 49/2023). We look at where your well and the surrounding ones are and, if any of them is a supply well, at its protection perimeter on the DGRH map viewer.
How much land is needed to irrigate with the treated water?
25 m² of green area per population equivalent (art. 70.12 of the Balearic Water Plan, Royal Decree 49/2023), and in a home each bed space counts as one: a house with 8 bed spaces needs 200 m². On a finca in Sencelles land is not usually the problem; what we look at is where that area lies in relation to the wells.
It's a weekend house: does a treatment plant work if it isn't used every day?
Yes, if the unit is chosen for that use. An aeration treatment plant keeps its biology alive with the blower running; the important thing is not to cut the power when the house is empty. Servicing is as the regulations set or, if the manufacturer requires more, as the manufacturer says: on the GRAF one2clean, as an example, twice a year. It is what we recommend for the country houses of Sencelles used at weekends.
Who files the paperwork for the treatment plant of a house in Sencelles?
Your architect or your engineer. The responsible declaration is filed with the Direcció General de Recursos Hídrics, with proof of purchase and installation, the technical specifications, the performance and the maintenance plan (art. 70.4 of the Balearic Water Plan, Royal Decree 49/2023). We prepare and sign that documentation as the installation company and hand it over to them.
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 Sencelles with no mains sewer?
Send us the location, the number of bed spaces, where the well is and a few photos. We reply within 24-48 hours on working days.