I. Water Supply Networks and Facilities
Topic I.3. Sources for Water Supply - Surface Waters and
Groundwater : Quality and Peculiarities
Water Quality
General classification of water quality parameters:
 Physical - temperature, transparency, turbidity, colour, smell, taste,
conductivity, suspended solids
 Chemical - dry residuals (total, soluble), hardness, alkalinity, pH,
oxidability, gas saturation
 bacteriological and biological - pathogens, coli-index, coli-test, etc. and
hydrobionts, algae, fitoplancton, zooplancton, etc.
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Water Quality
A. Physical Water Quality Parameters
 Temperature
Rivers - 0o - 26o C
Lakes - relatively constant (equal to the mean air temperature)
Bulgarian State Standards (BSS) - 6o - 12o C (degree santigrade)
 Transparency/Turbidity
Snelen’s type (symbol) - for transparency (30 cm according to the BSS)
Suspended solids concentration, SS (SS < 2 mg/l according to the BSS)
 Colour
Platinum-cobalt scale (solution of K2PtCl6 and CoCl2 in H2SO4)
Roubliov’s scale (solution of K2CrO2 and CoSO4), [degree];For natural
waters - 10 - 20; For drinking water < 30 degree according to the BSS 2
Water Quality
 Taste
Salty, sweet, bitter, sour (no any taste is permissible in drinking water)
 Smell
Aromatic (pleasant), hydrosulfuric (H2S), phenolic, marsh, chloric (Cl2);
5-grade scale (based on probe dilution) is applicable for smell detection;
smell < 2 degree is permissible for drinking water according to the BSS
B. Chemical Water Quality Parameters
 Dry residuals (DR)
DR < 1000 mg/l is the standard limit for drinking water accord. to the BSS
 Non-organic residuals (NOR)
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Water Quality
 Hardness
It is due to presence of Ca2+ and Mg+ salts of carbonic acid (temporal
hardness) and/or Ca2+ and Mg+ salts of strong acids (permanent
hardness)
Measures - mg-equiv./l, degree (German, French and English); 1o Germ. =
10 mg/l CaO
According to the BSS, hardness > 25o Germ. is not permissible for
drinking water
 Alkalinity
It is due to presence of HCO3-, CO32-, K2SO4, Na2SO4,KCl, NaCl
 pH (active reaction)
H2O  H+ + OH[H+] = 10-7 mol/l - neutral
pH = -log[H+] = -log(10-7) = 7 - neutral active reaction
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Water Quality
 Oxidability
Measure - the mass of KMnO4, necessary for oxidation of the organic
substances in a unit water volume, [mg/l]
Standard limit - 2,6 [mg/l]
 Content of Fe2+ and Mn+
In groundwater Fe2+ and Mn+ are usually in the form of Fe(HCO3)2 and
Fe(HCO3)2 , respectively
On the surface: 4Fe(HCO3)2 +O2 + 2H2O = 4Fe(OH)3 + 8CO2
4MnHCO3 + O2 + 2H2O = 4MnOH + 4HCO32The Fe(OH)3 and MnOH create a bitter taste and a black colour of water
Standard limits:0,2 mg/l for Fe(OH)3 and 0,1 mg/l for MnOH, respectively
 Carbonic acid balance
4HCO32-  CO32- + CO2 + H2O
The above balance depends strongly on pH value
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Water Quality
 Dissolved gases
CO2 presents in natural water at pH < 8,3
O2 concentration depends on water temperature and atmospheric
pressure
H2S (and/or its ions HS- and S2- in ratio, depending on pH and
temperature) present in some groundwater
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Water Quality
C. Bacteriological and biological water quality parameters
 Bacterial content
Bacteria general division: pathogens (creating illness); saprophytes (nonharmful)
Esherihia Coli - a saprophyte, accommodating at the human stomach and
faeces is an indicator for faecal pollution of water
Measures: coli index - number of the coli-bacteria in 1 l water volume;
Standard limit: coli index < 10
 Biological content
General division: Fauna - zooplancton (suspended), bentos (sediment),
hydrobionts (attached); Flora - phytoplancton (suspended), algae
(suspended, rooted)
Saprobility (symbioses): polysaprobe, mezosaprobe ( and ) and
oligosaprobe
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Water Supply Sources Peculiarities
A. Surface Waters: Rivers
 Source of feeding - atmospheric water and groundwater
 Runoff regime - great variety of flowrates and water levels
Water intake
category
I
Water level security, %
min
max
1
97
II
III
3
95
5
90
 Water quality - depends on geological, climatic and anthropogenic factors
 Erosion and silt regime
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Water Supply Sources Peculiarities
B. Surface Waters: Lakes and Reservoirs
 Stratification in depth
I zone (0 - 4 m) - higher temperature and pollution, low O2 concentration,
plankton development
II zone (under 4 m) - lower temperature (1o C decrease in every 1 m
depth), highest O2 concentration
III zone (above the bottom) - lowest temperature and O2 concentration,
high H2S, Fe2+ and Mn+ concentrations
 Water quality
It depends on: geological features of the catchment and the lake bottom;
anthropogenic impact; evaporation (increasing water salinity),
euthrophication (phytoplankton “blooming”).
 Silting
(The “dead” volume filling)
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Water Supply Sources Peculiarities
C. Groundwater
General classification:
I. According to the salinity (mineral salts content)
 Fresh (sweet) water - up to 1 g/l dry residuals
 Slightly mineral water - 1 - 3 g/l dry residuals
 Average mineral water - 3 - 10 g/l dry residuals
 Mineral water - 10 - 50 g/l dry residuals
 Strong mineral water - above 50 g/l dry residuals
II. According to the temperature
 Very cold water - about 4o C
 Cold water - 4o - 20o C
 Hot water - 20o -37o C
 Warm water - 37o - 42o C
 Very warm water - 42o - 100o C
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Water Supply Sources Peculiarities
III. According to the hydrogeological conditions
 Shallow aquifer (water-bearing stratum) -less than 10 m
 Deep (10 - 30 m) non-pressurised aquifer - over impervious
layer (clay)
 Deep (10 - 30 m) pressurised aquifer - between two
impervious layers
IV. According to water location
 At the river terrace (send, gravel)
 At the rock cracks
 Springs - water coming out of pressurised or nonpressurised aquifers
 Artesian water - coming out of pressurised aquifer and with
piesometric head above the ground level
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