Water is omnipresent on Earth as it covers 72% of its surface (97% salt water and 3% fresh water). Water is the living environment for many species and is necessary for all life to thrive and survive. It is also a major part of human economy, for it can be used as a solvent, washing agent, cooling agent, or raw material for industrial purposes.
Water is liquid at ambient temperature and pressure, colorless, odorless, tasteless, and neither volatile nor toxic. Water molecules are composed of one oxygen atom and two hydrogen atoms (H2O). Despite its apparent simplicity, water possesses exceptional physical and chemical properties that explain why it is involved in all major industrial processes.
In actual fact, pure water does not exist. Different types of water can be found: bottled water, spring water, mineral water, natural mineral water, urban waste water (UWW), industrial waste water (IWW), distilled water, demineralized water, permuted water, and milli-Q® water.
Each type of water is a complex solution containing, in addition to water molecules:
- Ionic mineral species less than 1 nm in size. We generally distinguish metal ions (Ca2+, Mg2+, Na+, Fe2+) from halide ions (F-, Cl-), sulfate ions (SO42-), nitrogeneous substances (NO3-, NO2-, NH4+), phosphoric substances (orthophosphates like H2PO4-, HPO42- and PO43- ) and carbonaceous substances (HCO3-);
- Oxidizable organic matter (O2, CO2, proteins, lipids, carbohydrates, carbonaceous or nitrogenous organic matter) and inorganic oxidizable matter;
- Settleable suspended matter (sand particles, organic debris) or non-settleable (colloidal particles, limes, microscopic organisms). “total suspended solids” (TSS).
Bottled water is water packaged in bottles and intended for human consumption
Spring water naturally meets drinking water standards and is bottled without any chemical treatment. It does not have any therapeutic properties.
Mineral water drinking water of underground origin. It is generally produced for commercial purposes.
Natural mineral water in France receives its title from the medical academy for its therapeutic virtues. It does not necessarily respect drinkability standards.
Urban waste water (UWW) is domestic sewage water (increasingly including rain water). It is characterized by a relatively constant composition (high density of organic or nitrogeneous matter).
Industrial waste water (IWW) is waste water generated by industrial activities (this generally excludes rain water, unless it is polluted by runoff or soil from active or abandoned industrial sites). These waters contain diverse chemicals (nitrogen compounds, hydrocarbons, metal salts, etc.), depending on the industrial activity.
Distilled water is water that has been distilled once or several times. Theoretically, it no longer contains certain mineral or organic species we might find in natural water. It contains dissolved gases like O2 and CO2. Its pH at ambient temperature is about 5.4.
Demineralized water is water that in principle no longer contains ions (calcium, magnesium, sodium, potassium, sulfate, chloride...), having passed through an ion exchange resin. However, uncharged matter may remain (such as organic or inorganic matter, bacteria etc…). This type of water is also called deionized water.
Deionized water is not as “pure” as distilled water.
Permuted water is water without any calcium or magnesium ions. It is obtained using an ion exchange resin. Calcium and magnesium are replaced by sodium and potassium ions. Permuted water is therefore not as “pure” as deionized water.
milli-Q® water is purified through a filter/resin/membrane system. It no longer contains ions and almost no organic species are present; it is ultra-pure water.
We can determine the total suspended solids (TSSs) by a turbidity measurement (nephelometric measurement): we measure the amount of light scattered by colloidal particles at an angle of 90°, from an incident beam of wavelength 860 nm. Turbidity measurements are governed by the NF T 90-033 and ISO 7027 standards.