Running mineral water delivered to our homes is a readily available convenience that requires the implementation of highly advanced processes and technologies to treat, transport, and guarantee the potability of the water all the way to our taps. From source to consumption, discover the journey of water to our homes and the various treatment stages involved in making our drinking water safer for our health.

Where does the water we drink come from?

Tap water comes from surface water (41%) and groundwater (61%). Groundwater is located in aquifers of varying depths and originates from rainwater infiltrating the subsoil. Drilling a well is necessary to access it. Surface water used for drinking water comes from watercourses (rivers, streams, lakes, ponds) or natural or artificial reservoirs. It is usually extracted by pumping, most often upstream of the towns and cities it serves.

Three characteristics are taken into account when choosing a water resource to use:

• Resource availability: groundwater or rivers must provide sufficient water.
• Resource quality: higher quality resources with good protection against pollution are used first. Degraded or poor quality resources are discarded. Groundwater is preferred to surface water.
• Security of supply: a substitute or backup resource must be provided in case a water point becomes unavailable.

From source to tap: the domestic water cycle

Drinking water travels through a complex circuit that carries it from the production plant to the consumer’s tap, passing through the water reservoir. This entirely artificial circuit is called the domestic water cycle. Developed in the 19th, its purpose is to collect water, treat it if necessary to make it potable, and make it readily available in homes simply by turning on the tap. Furthermore, it allows for the purification of dirty water so that it can be returned to nature without harming waterways and the environment. This cycle consists of six stages:

1) Pumping or extraction: water is taken by pumping from rivers or underground water tables.

2) Water treatment or purification: in order to meet drinking water and quality standards, water from rivers and groundwater is treated to remove impurities, microbes and viruses.

3) Storage: Once treated, the water is sent to reservoirs. These are either underground or elevated. When they are elevated, they are called water towers. The location of the water tower at the highest point of the town or village ensures sufficient pressure throughout the network and allows the water to be distributed by gravity.

4) Distribution: The water is then transported through pipes to individual homes. The drinking water distribution network comprises 850,000 km of pipes running from reservoirs to subscribers, equivalent to 21 times the circumference of the Earth. The water will be used for various purposes, including cleaning, cooking, and laundry.

5) Cleaning or depollution: After use, wastewater laden with domestic pollutants is collected and then sent to a wastewater treatment plant to remove organic and chemical pollution. The treatment process involves removing suspended solids (sand, various waste materials, etc.) as well as organic matter from the water.

6) Replenishment: the treated water (clean but not potable) is then released into the natural environment.

The stages of water treatment

Before reaching the tap, water must be treated to make it potable. Indeed, most surface water is unfit for consumption because it is laden with impurities carried by runoff, such as mineral debris (sand, silt, etc.) or organic matter . In contrast, groundwater is of better quality because it benefits from the natural filtering action of the soil.

Carried out in a drinking water plant, the treatments vary depending on the origin and quality of the water. Whether preventive or curative, they all follow the same principle: eliminating the elements of matter contained in the water through successive stages, down to microscopic organisms such as viruses and microbes.

The production of drinking water includes the following steps:

• Screening: upon entering the factory, the water passes through a grid of bars, spaced approximately 5 cm apart, which stops the largest debris (branches, plastics, etc.).
• Sieving: the water continues its path and passes through a finer mesh, the sieve, which retains small debris such as cigarette butts, dead leaves,
• Flocculation or sedimentation: a coagulant is added to the water to clump together the remaining debris (dust, soil particles, fish eggs, etc.) into flocs. These flocs, being heavier than water, settle to the bottom of the settling basin, and 90% of the suspended matter is thus removed as sludge. The aim of this step is to make the water clear.
• Filtration: To further clarify the water, it is passed through a bed of sand 80 to 150 cm thick. Sand bed filtration retains the last invisible but still present suspended particles in the water. Bacteria attached to the sand grains break down organic matter.
• Ozonation : the water is disinfected using ozone, which has bactericidal and antiviral properties. This gas, mixed with the water, also acts on organic matter by breaking it down. It also improves the color and taste of the water.
• Activated carbon filtration: the activated carbon grains remove organic matter that could generate bad tastes and retain micro-pollutants such as pesticides.
• Disinfection: the final step in the process, it eliminates microorganisms that can pose a health risk. Several disinfection techniques exist, but the most well-known is chlorination. This involves adding chlorine gas or bleach at the water treatment plant and at various points in the distribution network. The goal is to prevent bacterial growth and maintain water quality throughout its journey through the pipes.

To guarantee its quality, the distributed water is monitored throughout its journey, from the source to the home, by the Regional Health Agency (ARS). Strict health monitoring is carried out at the pumping station, the treatment plant, the distribution network, and at consumers’ taps to verify that it meets the standards set by European and World authorities.