Drinking water supply

There are three resources for producing drinking water:

  • Surface water: reservoirs and rivers.
  • Underground water: wells and springs.
  • Sea water and brine.

The drinking water supply consists of taking in untreated water, treating it for drinking and distributing it for consumption. Surface, underground and sea water and brine are used, taken in with pumping systems that control the amount of water supplied to the plant.

Screens are installed in the intake to remove wastes and plant life. To convert these resources into drinking water, the untreated water must be taken in and given a more or less complex treatment depending on its quality.

This process is carried out in drinking water treatment plants and involves the following stages.

Stage 1. Mixing chamber.
This is a tank in which the untreated water is mixed with chemical reagents for treating it, using mechanical equipment or a stirrer.

pH adjustment: the dose of this reagent depends on the acidity and mineralisation of the water to be treated.

Oxidant: this reagent oxidises the compounds in the water which precipitate and are removed from the natural water. At the same time, this helps to remove microorganisms that are harmful to persons. The oxidants currently used are ozone, potassium permanganate and chlorine.

Coagulant: this destabilises the solids suspended in the natural water which start to agglomerate. It helps to inhibit certain organic compounds. The main coagulants used are aluminium sulphate, ferric chloride and aluminium polychloride.

Stage 2. Flocculation chamber.
This consists of various tanks in series where the agglomeration of particles is accelerated so that they reach a density that is greater than that of the water, helped by mechanical blades. Generally, at the start of this stage a reagent known as a flocculant or auxiliary polymer is added to help with the formation of larger and heavier particles, increasing the elimination of solids.

Stage 3. Clarifiers.
Most of the organic and metallic components and suspended solids are removed from the water in this process which consists of a series of tanks in which the particles settle by gravity.

Stage 4. Filters.
This phase involves refining to eliminate the lighter and smaller particles not removed in the previous process.

It consists of a series of chambers containing filtering material through which the water passes. The filtering material consists of sand with a grain size that is defined by the quality of the water to be treated. Depending on the water's quality, the sand filtering stage can be completed with filtering in activated carbon to remove pesticides, flavours and odours.

Stage 5. Disinfection.
After filtering, a disinfectant is added to the water to guarantee its microbiological quality and convert it into drinking water for human consumption. Once produced, the drinking water is stored in tanks before being supplied to consumers.

Storage of drinking water in tanks
These guarantee the supply of drinking water regardless of the production capacity and the consumers’ demand. The drinking water is stored in tanks that allow the available volume of water to be adjusted and regulated.

As a general rule, the tanks are located at high points to allow distribution by gravity without the need for pumping.

Supply system
The drinking water stored in the tanks is supplied to consumers through the supply system.

Care and attention is fundamental in the supply system to:

  • Event any leaks that would cause a loss of drinking water.
  • Identify as soon as possible any fault that could interrupt the supply.
  • Repair or replace as soon as possible any defective channelling to guarantee the quantity and quality of the water supplied to consumers.
  • Carry out improvements to guarantee the supply.
  • Maintain the level in the tanks to ensure an optimal water supply.