Water is omnipresent on Earth as it covers 72% of its surface (97% salted water and 3% fresh water). Water is the living space of 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 solvent, washing agent, cooling agent, or raw material for industrial purpose.
Water is liquid at ambient temperature and pressure conditions, colourless, odourless , tasteless, and neither volatile nor toxic. Water molecules are made of one oxygen atom and two hydrogen atoms (H2O). Despite its apparent simplicity, water possesses exceptional physical and chemical properties that explain its implication in many industrial processes.
In fact, pure water does not exist. Different types of waters are catalogued on Earth: bottled water, spring water, mineral water, natural mineral water, residual urban waters (RUWs) or residual industrial waters (RIWs), distilled water, demineralised water, permuted water, milli-Q® water.
Each type of water is a complex solution containing, in addition to water molecules:
- Ionic mineral species inferior to 1 nm in size. We generally distinguish metal ions (Ca2+, Mg2+, Na+, Fe2+), from halide ions (F-, Cl-), sulfate ions (SO42-), nitrogen ions (NO3-, NO2-, NH4+), phosphorus ions (orthophosphates like H2PO4-, HPO42- and PO43- ) and carbonated ions (HCO3-) ;
- Oxidizable organic matter MOOX (O2, CO2, proteins, lipids, carbohydrates, carbonated or nitrogenous organic matter) and inorganic oxidizable matter MIOX;
- Settleable suspended matter (sand particles, organic debris) or non-settleable (colloidal particles, limes, microscopic organisms). We talk about « total suspended matter » (TSM).
Bottled waters are waters conditioned in bottles and destined for human consumption
Spring waters are naturally compatible with drinking water standards and bottling standards without chemical treatment. They do not display therapeutic properties.
Mineral water is a drinking water from underground origins. It is generally part of a commercial business.
Natural mineral waters in France receive their title from the medical academy for their therapeutic virtues. They do not necessarily respect the drinkability standards.
Residual urban waters (RUWs) are domestic sewage waters (including more and more rain waters). They have a relatively unchanging composition (high density of organic or nitrogen matters).
Residual industrial waters (RIWs) are waste waters generated by industrial activities (this generally excludes rain water, excepted if these rain waters are contaminated by water runoff or used or abandoned industrial soil). 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 does not contain some of the mineral or organic species we might find in natural water anymore. It contains dissolved gases like O2 and CO2. Its pH at ambient temperature is about 5.4.
Demineralised water is theoretically a water without any ions (calcium, magnesium, sodium, potassium, sulfate, chloride...) This result is achieved with a passage through an ion exchange resin. However, uncharged matters may remain (such as organic or inorganic matter, bacteria etc…). This type of water is also called deionised water.
Deionised water is not as pure as distilled water.
Permuted water is water without any calcium or magnesium ions. It is obtained using a ion exchange resin. Calcium and magnesium are replaced by sodium and potassium ions. Permuted water is therefore not as pure as deionised water.
milli-Q® water is purified through a filter/resin/membrane system. It does not contain any ions and almost no organic species anymore; it is ultra-pure water.
We can determine the total suspended matters (TSMs) through a turbidity measurement (nephelometric measure): we measure the amount of light scattered by colloidal particles at an angle of 90°, from an incident beam of 860 nm wavelength. Turbidity measures are governed by the NF T 90-033 and ISO 7027 standards.