Well water: testing and potability
Well water is not potable simply because it comes from underground, and to use it for human consumption it must be tested by an accredited laboratory covering microbiological parameters, nitrates, conductivity and metals, with periodic repetition.
gelisted editorial team · Updated 15 August 2026
The short version
- A basic potability test costs 80 € to 200 €.
- Nitrates are the parameter that most often fails in farming areas.
- Microbiological contamination can appear after heavy rain.
- In coastal areas conductivity must be watched for saline intrusion.
Clear water with no smell tells you nothing about whether it is safe. The two most common problems are invisible, tasteless and odourless.
What to test
The microbiological block, with indicator bacteria of faecal contamination, which determines the acute risk. Nitrates, usually agricultural or from septic tanks. Conductivity and chlorides, which reveal saline intrusion in coastal areas. Metals such as arsenic or lead according to local geology. And general parameters such as pH, hardness and ammonium, which indicate the state of the aquifer.
| Parameter | Usual origin | Frequency |
|---|---|---|
| Indicator bacteria | septic tanks, livestock, rain | twice a year |
| Nitrates | agriculture and septic tanks | annual |
| Conductivity and chlorides | saline intrusion | annual |
| Metals | local geology | every 2 or 3 years |
| pH and hardness | local geology | annual |
| Basic test | accredited laboratory | 80 to 200 € |
| Full test | accredited laboratory | 250 to 600 € |
How often to repeat it
At least once a year, with a second sample after the first heavy autumn rains, because surface run off can introduce contamination into poorly protected wells. Also repeat after any nearby construction work, after any change in taste or colour, and always before using the water for small children or vulnerable people.
Taking the sample
In a container supplied by the laboratory, not a reused bottle. Let the water run for 2 or 3 minutes before filling. Do not touch the inside of the cap or the container. And deliver it within the stated time, usually under 24 hours and chilled for the microbiological block. A badly taken sample produces false positives and means paying for the test twice.
Recording the exact time of sampling is part of the procedure and the laboratory asks for it on the form.
If the result fails
For microbiological contamination, disinfection by chlorination or ultraviolet lamp, after checking the wellhead, the cover and the distance to septic tanks. For high nitrates, reverse osmosis at the point of use, since boiling does not remove them. And for saline intrusion, review the extraction rate, because over pumping makes it worse. In all cases, use the water for irrigation and another source for drinking until it is resolved.
Frequently asked
+Is well water drinkable?
Not by default. It requires testing by an accredited laboratory before use for human consumption.
+What should be tested?
Microbiological parameters, nitrates, conductivity and chlorides, metals by area, and pH and hardness.
+How often?
At least annually, with a second sample after the first heavy autumn rains.
+What does it cost?
Eighty to two hundred euros for a basic test and 250 € to 600 € for a full one.
+Does boiling remove nitrates?
No. Reverse osmosis at the point of use is required.
Sources
- 1Ministerio de Sanidad, Gobierno de España (August 2026)
- 2Govern de les Illes Balears, Govern de les Illes Balears (August 2026)