Water quality: a challenge of precision and responsibility
When we talk about water quality, we often refer to whether it is drinkable or not. But this concept is much more complex than it might seem at first glance. The quality of water for human consumption is measured using physical, chemical and biological parameters, included in the current regulations (Royal Decree 3/2023, of January 10), which establishes the maximum permitted values, the required analytical sensitivity and the precision of quantification.
A look at the physical parameters
The physical parameters include temperature, turbidity, colour, and electrical conductivity (an indicator of salinity). Measurements such as transmittance and absorbance are also included, indicating the water’s ability to let through or absorb ultraviolet light. The more light that passes through the sample, the purer the water is considered.
The chemical world of water
Chemical parameters evaluate the presence and concentration of dissolved substances. The most significant include:
Dissolved salts: Ions such as sodium, calcium, magnesium or potassium (cations), and chlorides, bicarbonates, nitrates or sulphates (anions).
Radionuclides: The regulations require the quantification of radioactivity using parameters such as alpha and beta activity, tritium, radon and indicative dose.
Substances of natural or metabolic origin: Humic and fulvic acids, chlorophyll, algal toxins or hormonal residues from wastewater may appear in surface waters.
Synthetic pollutants: A wide range of industrial compounds, such as biocides, solvents or pharmaceuticals. Perfluoroalkylated and polyfluoroalkylated substances (PFAs) stand out, known as forever chemicals due to their persistence in the environment.
Biological indicators
Biological parameters focus on the detection of microorganisms that can cause diseases. Microbiological indicators are used, especially those that reveal faecal contamination. These microorganisms must be absent in at least 100 millilitres of water. Current regulations include bacteria (such as coliforms or enterococci), but also viruses (somatic coliphages) and protozoa (such as Cryptosporidium).
The analytical revolution
The progress seen in analytical chemistry since the 1960s has been spectacular. According to Dr Rhodes Trussell, the precision of analytical techniques has increased by three orders of magnitude every twenty years (Trussell, 2013, address given as part of the Clarke Awards ceremony, at the National Water Research Institute in California, United States). This means that substances once detected in milligrams per litre can now be found at levels of nanograms per litre: a million times greater resolution.
How extreme is this precision?
To detect 1 nanogram per litre (ng/l) of sugar in water, we would have to dissolve an 8-gram sachet of sugar in 8 billion litres of water. This is equivalent to filling a football field with a column of water 1,000 meters high. Such sensitivity has forced us to constantly review the thresholds considered safe for human health, especially since the level of toxic effects or temporary exposure is still unknown for many substances.
Towards indispensable purification
In a context of demographic pressure, climate change and the worsening quality of supply sources, regulations increasingly require purer water, which increases the complexity of the treatment and management of the waste generated. The substances eliminated often return to the environment, which complicates drinking water treatment for systems that capture water downstream.
Faced with this challenge, purification emerges as a key solution. Facilities such as the Abrera and Sant Joan Despí DWTPs, which supply much of the metropolitan area of Barcelona, already use advanced technologies to treat surface water with a high pro portion of treated effluents, especially in situations of drought.
The incorporation of purification and real-time monitoring systems within the water cycle not only ensures regulatory compliance, but also allows resources such as regenerated water to be recovered. This approach will be essential to guarantee supply in a 21st century marked by hydrological uncertainty.
The incorporation of purification and real-time monitoring systems ensures regulatory compliance and allows resources such as regenerated water to be recovered.
