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Water Quality

1. EPAL’s Water

EPAL is proud to deliver quality water to your house every day!

The quality of the water supplied by EPAL is guaranteed by the quality of the sources (surface water and groundwater), by the various treatment processes to which the water collected is submitted and also by the quality control of the water carried out throughout the supply system right up to the Customer’s tap.

This control is achieved through continuous monitoring equipment installed at strategic points in the supply system, as well as through laboratory analyses carried out by qualifiedtechnicians and using advanced technology.

Annually, EPAL carries out more than 200 thousand analyses in the control of the quality of water, having 99.9% compliance with national and european legal parameters. It carries out a number of analyses which is greater than that stipulated and monitors other non-obligatory parameters, aimed at ensuring the highest quality of water supplied.

However, the quality of the water delivered to the Customer at the entrance to their building can suffer alterations due to a lack of maintenance on the building and domestic network, particularly in the case of old or cast iron pipes.


Drink EPAL’s water… it’s reliable!

EPAL supplies water to around three million people. It is responsible for distribution in the City of Lisbon, with around 350,000 customers, and a further 34 Municipalities, ensuring the supply of quality water to all.

The quality of water supplied by EPAL is ensured through the treatment processes that the water is submitted to and by the monitoring carried out throughout the whole supply system, from the sources right up to the customer’s tap.

Water Treatment
To ensure the quality of the water right up to the customer’s tap, EPAL uses treatment technologies appropriate to the characteristics of the water extracted and carries out continuous water quality monitoring throughout the supply system.

The water extracted at the Castelo do Bode reservoir and treated in Asseiceira WTW passes through the following treatment stages: pre-oxidation with chlorine gas, remineralisation and acidity correction, coagulation, flotation, ozonation, filtration, pH correction and final disinfection.

In the case of water extracted at Valada Tejo, treatment is carried out in Vale da Pedra WTW and includes the following stages: pre-oxidation with chlorine gas, coagulation/ flocculation, sedimentation, filtration, correction of pH and final disinfection.
  • Pre-oxidation with chlorine gas | Chlorine injection to reduce the quantity of organic matter present in the water
  • Remineralisation and acidity correction | Intended toaddress the water’s excessive softness, creating a fine layer of calcium deposits which protect the inside of the water pipes from corrosion
  • Coagulation/Flocculation | Chemical process for the buildup of small suspended particles leading to the formation of floc, sufficiently large to ensure suitability for the subsequent sedimentation or flotation stage
  • Sedimentation | After coagulation/flocculation, the larger floc settle on the bottom of the sedimentation tanks, thus eliminating most of the suspended particles. The clarified water moves on to filtration
  • Flotation | In this stage of the treatment, the smaller floc are held together by air bubbles which facilitate their rise to the surface and later removal
  • Ozonation | Ozone is a strong oxidising agent and is used to eliminate algae and other organic matter, possessinganti-septic and bactericidal properties, with an important application in water treatment
  • Filtration | The water passes through sand or sand and anthracite filters, in which the smallest particles are trapped, making it possible to remove them from the water. Filtration clarifies the water and increases the effectiveness of disinfection
  • PH Correction | In this stage, the pH is adjusted, ensuringthis parameter remains within the range of values defined bylaw
  • Final Disinfection | Chlorine is added to ensure microorganisms do not develop, a residual content being maintained to guarantee water quality throughout the bulk supply network and distribution to the customer’s tap
Water Quality Control
On a daily basis, EPAL analyses and controls the quality of the water extracted, transported and supplied. This control is achieved through continuous monitoring equipment installed at strategic points in the system and through laboratory analyses carried out by qualified technicians and using advanced technology.

Annually, EPAL carries out thousands of analyses throughout the supply system, with the number of analyses undertaken being greater than that stipulated by law.

In the context of water quality control, the analyses carried out at customers’ taps in the city of Lisbon have more than99.5% compliance with the legal parameters defined by Decree-Law no. 306/2007, of the 27th of August.

The water quality control carried out within the EPAL supply system includes the following components:
  • Continuous monitoring of water quality parameters (e.g. chlorine, pH, total hardness, aluminium, turbidity,conductivity, alkalinity), undertaken at treatment works andin other strategic locations throughout the supply system,consisting of real time information processing that allowsimmediate action in abnormal situations
  • Water Quality Control Plan (WQCP) for the supply system that includes the following controls:
  • Water quality control at the sources to assess the evolution of water quality throughout its extraction, treatment, transport and supply system
  • Monitoring of the treatment efficiency in the various operations undertaken at the Vale da Pedra and Asseiceira WTWs
  • Monitoring undertaken in compliance with the legal requirements defined in Decree-Law no. 306/2007, of the27th of August, including the collection of water samples for analysis at the supply points to the Municipalities supplied by EPAL and at customer’s taps in the city of Lisbon
  • Operational control/monitoring to check water quality levels throughout the supply system and for the timely detection of any abnormalities, allowing preventive action to be taken
  • Complementary water quality control, undertaken through the processing of complaints, monitoring of the effectiveness of washing and disinfection operations of pipes and tanks, dealing with legal non-compliances and in monitoring water quality parameters which are not obligatory under national legislation
Company Laboratories
To analyse and monitor water quality, EPAL has several laboratories accredited under standard NP EN ISO/IEC 17025 for the processing of samples and for water quality tests:
  • Central Laboratory, accredited since 1999
  • Vale da Pedra Laboratory, accredited in 2008
The results of laboratory analyses carried out by EPAL in compliance with the legislation in force are available on Central Laboratory.

Water Sources
The water extracted is from surface water and groundwater sources:
  • Surface water extractions:
    • River Zêzere | Castelo do Bode Reservoir
    • River Tagus | Valada Tejo
  • Groundwater extractions:
    • Alenquer, Lezírias and Ota
In natural environments, water can appear clean, however it does contain impurities, so as a result all water extracted needs to be treated before being distributed. Therefore, EPAL has two water treatment works (WTW) where the water extracted at the Castelo do Bode reservoir and at Valada Tejo is treated.

The production capacity of the EPAL system is in the order of 1,000,000 m3/day of water for human consumption.


Water can occasionally smell and taste.This is due to various factors such as the presence of chlorine which is used in water disinfection and poor maintenance of building supply systems and home plumbing including taps. The taste also depends on the composition of its salts (such as, for example, calcium and magnesium).

To improve the taste and smell of water we put forward some very simple suggestions which certainly contribute to drinking water with more enjoyment.

  • In hot weather water temperature can rise in distribution systems or in buildings where they are exposed to the heat. Before drinking, let the water run for a while to freshen up
  • The fresher the water the better it tastes. Keep water in refrigerator, preferably in a closed receptacle. It helps to improve the taste and the sensation of freshness
  • Bootles and receptacles used to serve water should be washed frequently possibly using a little vinegar or salt rinsing well afterwards
  • Change regularly the water for ice cubes. If they remain unused for a long time it is better to get rid of them as they will acquire the tastes of food stored in the freezer
  • Do not use hot tap water for making tea or coffee. It is better to boil water for this as it eliminates the disagreeable taste of chlorine
  • Refrigerators that have a water tank and icemaker require special care and should be cleaned frequently
  • After a prolonged absence from home (holidays, for example) let the water run for a while before drinking or cooking

Tips for drinking more water

  • Drink water every day, and several times a day
  • Keep a jug or other recipient of fresh water near you during the day, for example at the kitchen door or by the side of the television
  • At night keep a jug on the bedside cabinet and remember to drink water before going to sleep
  • Always take a bottle of water when you leave the house or go for a walk
  • Drink water before, during and after physical activity to help maintain energy levels
  • Keep a bottle of tap water in the fridge as the low temperature helps to neutralise the smell or taste of chlorine
  • Add a slice of lemon or a leaf of mint so as to enjoy your drink more
  • If necessary, set your alarm clock for a time to drink water
Water is the main ingredient of all drinks, but drinking tapwater is the most efficient and accessible way.

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