ServicesWater Supply

The main purpose of the Water Supply Division is:

to ensure uninterrupted water supply with high quality drinking water and adequate pressure in the service area of EYATH S.A., while at the same time sustainably managing water resources.

In this context, domestic consumers, professionals, services and buildings of public interest (such as schools and hospitals) of Thessaloniki and the interconnected municipalities, industrial areas, the fire-fighting network and neighbouring Municipal Water Supply and Sewerage Companies are being supplied with water.

The individual operational objectives and responsibilities of the Departments of the Water Supply Network Division are formulated in order to achieve the main goal of continuous and quality water supply.

Water supply with high quality drinking water

For this purpose,

  • advanced water purification processes are implemented from Aliakmonas river to the Thessaloniki Water Treatment Plant (TWTP);
  • disinfection is carried out by chlorination of water from the springs of Aravissos and drilling at the Water Supply facilities (Pumping stations and Tanks);
  • continuous water quality controls and analyses are carried out from its source until it is made available to consumers, and
  • water supply with certified, safe and healthy drinking water is ensured in accordance with the legislation.

Uninterrupted supply of water of sufficient pressure

For this purpose,

  • continuous management and monitoring of water abstractions, water reserves, water supplies and flows is carried out with the contribution of SCADA systems;
  • emergency damage response is ensured on a 24/7 basis,
  • maintenance, repair and upgrading of the water supply network and facilities are carried out;
  • maintenance, repair and upgrading of the electromechanical equipment and automation systems are carried out;
  • the operation, maintenance and repair of the TWTP is supervised, and
  • actions are undertaken to reduce water losses.

Water Routes


The water supply needs of the service area of EYATH S.A., averaging about 260,000 cubic meters per day (2017 reference year), are covered through three water supply sources:

  1. the Aliakmonas River, through the Thessaloniki Water Treatment Plant TWTP (surface water),
  2. the Aravissos springs in the prefecture of Pella (source water), and
  3. drilling in the plain of Thessaloniki (groundwater).

Please find here detailed qualitative and quantitative information on the water supply sources of the service area of EYATH.

oi piges mas


EYATH S.A.’s territorial remit, within which it can provide its services and conduct its business, is reflected in the following Map. Today, the service area of the company includes the Thessaloniki city complex, adjacent areas, as well as areas close to the water sources of the company. According to the 2011 census, EYATH S.A. supplies water to a population of about 926,000, out of which 827,000 exclusively and 99,000 in an auxiliary capacity. At the same time, the EYATH network supports the firefighting needs as it supplies 685 fire hydrants and two forest tanks.

Ydr Oria Drastiriotitas Ydreusis Feb2019 2


The external Water Supply Network, which concerns large diameter pipes, extends over 460 km. The distribution pipes of the Water Supply Network extend over a length of 2,230 km, resulting in the total length of the EYATH’s water supply lines exceeding 2,690 km.

Data on the construction materials and the diameters of the water pipes used are presented in the following Tables.

Ydr Diktio A3 Feb2019
MATERIAL Length (km) Percentage (%)
PVC 892 33
Asbestos 809 30
Cast iron 330 12
Unknown 302 10
Steel 175 6
HDPE 122 5
Pre-stressed concrete 52 2
Polyethylene 17 1
Stanton 2 0
GRP 1 0
Diameter (mm) Length (km) Percentage (%) Diameter (mm) Length (km) Percentage (%)
Φ20 5 0 Φ280 4 0
Φ25 2 0 Φ300 61 2
Φ28 0 0 Φ315 10 0
Φ32 2 0 Φ350 8 0
Φ40 5 0 Φ355 17 1
Φ50 91 3 Φ400 14 1
Φ60 10 0 Φ450 1 0
Φ63 129 5 Φ500 24 1
Φ75 16 1 Φ600 26 1
Φ80 401 15 Φ700 37 1
Φ90 97 4 Φ800 61 2
Φ100 370 15 Φ1000 19 1
Φ110 624 24 Φ1100 14 1
Φ125 30 1 Φ1200 4 0
Φ140 10 0 Φ1250 1 0
Φ150 106 4 Φ1300 4 0
Φ160 112 4 Φ1400 6 0
Φ175 1 0 Φ1500 5 0
Φ180 0 0 Φ1600 0 0
Φ200 158 6 Φ1650 50 2
Φ225 10 0 Φ1700 9 0
Φ250 31 1 Unknown 117 4

Water Supply Facilities


Besides the pipe network, EYATH S.A. has an expanded network of facilities with Pump stations and Tanks as its main elements, to transfer water from its sources (R. Aliakmonas, Aravissos springs, drilling) and distribute it for final consumption. In particular, this network includes 41 Pump Stations and 45 Tanks.

Pumping stations are facilities where submersible or surface type pumps are used to mechanically lift the water. This is required either for water abstraction from underground aquifers or for the transfer of water from a given point to a higher altitude point where tanks are normally located. EYATH’s tanks operate as underground or overground water storage facilities. In this way, the relief of the ground is eliminated as a natural barrier, thus ensuring the service of high altitude villages or areas and facilitating water supply management under normal or extraordinary conditions. In general, the layout of Pump Stations and Tanks is made to optimise complex technical and economic criteria.

The total installed capacity at 41 Water Supply Pump Stations is greater than 30,000 kVA, while the average annual total energy consumed thereof is about 64,000,000 kWh. In addition, the total capacity of the basic tanks is 211,200 m3.


Effective disinfection of water using chlorine is among the critical functions performed in these facilities. By disinfection we mean the destruction of pathogenic microorganisms contained in water. Chlorination of water takes place on a 24-hour basis with modern technology (dosing devices, chlorinators) using mainly chlorine gas or sodium hypochlorite. This process is carried out in selected central facilities of EYATH S.A.

According to the legislation, water chlorination is carried out in such a way that a small amount of residual chlorine remains to deal with infections when distributing water to consumers. This small amount of residual chlorine is completely harmless to human health. The disinfection of the distribution network of the Thessaloniki city complex is checked daily by the Water Supply Laboratory.

You can find more information about residual chlorine and the possible chlorine odour here.


EYATH S.A. has control centres for its facilities for the uninterrupted management and monitoring of water abstractions, reserves, water supplies and flows. They continually gather information about the parameters and operating characteristics of the facilities and the Water Supply Network. These capabilities are provided through the use of metering instruments, sensors and appropriate telecommunication and mechanical components interconnected and implemented through SCADA systems. The company’s control centres are staffed on a 24/7 basis.


An important link for the water supply of Thessaloniki from the Aliakmonas River is the Thessaloniki Water Treatment Plant (TWTP) of EYATH S.A., located 2 km from the industrial area of Thessaloniki in Sindos. The TWTP began its operation in August 2003 and has a processing capacity of 150,000 m3 per day at the current phase (1st phase). A study is currently being carried out to expand treatment by an additional 150,000 m3/day. When fully deployed, the TWTP will be able to treat 600,000 m3/day.

It is a modern industrial unit using an automated production process with a large number of on-line instruments, which continuously record operating parameters and water characteristics at the various stages (such as as flow meters, pH meters, conductivity meters, turbidimeters, chlorine residue counters). The readings of these instruments are sent to the TWTP Control Centre, which features a supervisory control and data acquisition (SCADA) system. The automatic operation of the TWTP’s units is achieved by using twenty two programmable logic controllers (PLCs).

Using the SCADA system allows:

  • continuous recording and control of water characteristics at the various treatment stages,
  • control of proper operation of individual units and equipment,
  • possibility of interventions to operating parameters for process optimisation,
  • ensuring the best quality of water at the TWTP’s exit.

In short, water treatment includes the following stages:

The 4,500 m3 TWTP tank, which regulates its operation, is fed from the Sindos Pumping Station, through a 5 km pressure pipe.

Water initially undergoes automatic pH correction, by addition of CO2.

The water to be treated enters the preozonification tanks, where it comes into contact with ozone (O3) produced in the ozonification unit. The tanks are airtight and the excess ozone-air is led to a destroyer. The two contacting tanks (one in operation in phase A) have a usable volume of 165 m3 each and the water stays there on average for 1.5 minutes.

The water enters the six parallel rapid mixing tanks (three in operation in phase A), where complete admixture and dispersion of the added flocculant solution (Aluminium polychloride, PAC) is achieved. The main objective of the process is the oxidation of the natural organic load, disinfection, algae reduction and achieving the optimal conditions for the operation of flocculation and sedimentation.

There are three circular flocculation-sedimentation tanks, with a diameter of 30 m and a lateral depth of 4 m. At the centre of each tank, there is a concentric cylindrical flocculation tank with an internal diameter of 9.60 m and a useful volume of 330 m3. The water enters from the bottom of the flocculation chamber and comes into contact with a polyelectrolyte solution, in order to form larger aggregates and achieve water clarification. The water-flake suspension from the flocculation chamber overflows into the main sedimentation tank, where resting conditions prevail, and the sludge flakes settle, while the clarified water follows an upward course. The bottom of each tank has a gradient of 1:8, to facilitate the transfer of settled sludge to the centre. The sludge and floating elements are swept using a gantry crane mechanism. The main objective of the process is to reduce suspended solids, algae, the organic load and remove floating elements.

Filtration takes place in rapid charge gravity filtration beds. There are nine twin monolayer (sand) beds and two single bilayer (sand-anthracite) beds. The twin beds have a total filtration surface of 78.75 m2; they are 2×3.15 m wide and 12.50 m long each. When a filtration cycle is completed, the bed is automatically washed with water and air. The filtered water is led to a clean water tank with a useful volume of 393 m3, which serves the pumping stations for washing the sand beds and the activated carbon and various other auxiliary functions. The main aim of the process is to reduce suspended solids (turbidity).

After leaving the clean water tank and following the addition of hydrogen peroxide (H2O2), the water enters the 990 m3 ozone contact tank. Ozone is produced by three generators, two for ozonification and one for preozonification, which operate based on the principle of electric discharges. The generators are supplied with dry, filtered air for the production of which two air compressors, two aftercoolers, two air chambers and two dryers are used. The main aim of the process is the oxidation of the organic load and the removal of odours and taste.

The activated carbon bed complex includes eight twin beds, each 2×3.15 m wide, 12.5 m long and with a layer depth of 2.50 m. The beds are cleaned using an air-water wash cycle. The main aim of the process is the adsorption and biodegradation of organic substances and the removal of odours and taste. To increase the adsorption capacity of carbon, Granular Activated Carbon (GAC) is thermally regenerated in a special rotating furnace unit with high temperature heating.

It should be noted that the EYATH’s TWTP is the only facility in Greece that includes adsorption in activated carbon beds and its regeneration in its process stages.

Water chlorination is conducted using a pair of interconnected chlorine gas cylinders, evaporators, chlorinators, chlorine injectors, as well as probes and a leak elimination tower. The main aim of the process is to destroy pathogens, prevent the development of microbiological pollution in the outflow tank and ensure residual chlorine in the distribution network.

To correct the pH, an emulsion is first produced by solubilising the calcium hydrate powder and a saturated solution is then formed in the saturation-sedimentation tank. The main aim of the process is to correct the pH to set values, to avoid unwanted deposits in the distribution network.

In the final stage, the treated water enters the two chambers of the outflow tank, which has a total capacity of about 80,000 m3.

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