Knowledge Base Rubricator

Water quality criteria

To evaluate water quality in rivers and water bodies, they are broken down into a few classes according to their contamination. These classes are based on the range of water pollution indices (WPI) that represent an aggregate index based on several factors, such as concentration of pollutants (nitrates, nitrites, ammonium nitrogen, heavy metals, petroleum products, etc.), characteristics of hydrobionts (aquatic organisms), trophicity and saprobity of water bodies.

Contamination classes

in the brackets WPI is given

  • very clean (< 0.25)
  • clean (0.25 .. 0.75)
  • moderately contaminated (0.75 .. 1.25)
  • contaminated (1.25 .. 1.75)
  • muddy (1.75 .. 3.00)
  • very muddy (3.0 .. 5.0)
  • extremely muddy (> 5.0)

Dissolved solids concentration (salt content)

Total Dissolved Solids is a measure of dissolved substances (inorganic salts, organic substances) contained in water. Also, this measure is called the dry solids content or total salt content. When estimating Total Dissolved Solids, solute gases are not taken into consideration.

The most contribution to Total Dissolved Solids is made by most common inorganic salts (bicarbonates, chlorides and sulfates of calcium, magnesium, potassium, and sodium) and small quantity of organic substances.

As a rule, TDS is calculated in terms of milligram per liter (mg/l); however, taking into account the fact that the unit “liter” is not an in-system unit, it would be more properly to express TDS in terms of mg/dm3, or gram per liter (g/l, g/dm3) in case of high concentration. In addition, salt content can be stated in particles per million (ppm) of water. The ratio between units in mg/l and ppm is nearly equal, and for the sake of simplicity it can be taken that 1 mg/l = 1 ppm.

Depending on total dissolved solids, waters fall into the following types:

  • subsaline/brackish (1-2 g/l),
  • of low salinity (2-5 g/l),
  • of medium salinity (5-15 g/l),
  • of high salinity (15-30 g/l),
  • brine (35-150 g/l),
  • heavy brine (150 g/l and over).


Component

Lowest concentration limit

Water type

Total Dissolved Solids (g/l)

2,0

Below 2.0 — subsaline/brackish

2,0—5,0— of low salinity

5,0—10,0— of medium salinity

10,0—35,0 — of high salinity

35,0—150,0— brine

over 150,0 — heavy brine

ΡΞ2 (dissolved form) (g/l)

0,5

0,5—1,4— low carbonate

1 ,4—2,5 — mean-concentration carbonate

over 2,5 — high carbonate

H2S general

(H2S+HS-2) mg/l

10

10,0—50,0 — low-sulfide

50,0-100,0 — mean-concentration sulfide

100,0—250,0— strong sulfide

 

250,0—500,0 — very strong sulfide

over 500,0 — ultra-strong sulfide

Arsenic ( As )

mg/l

0,7

0,7—5,0 — arsenious

5,0—10,0 — strong arsenious

over 10,0— very strong arsenious

Fe 2+ + Fe 3+ Tg/l

20

20,0- 40,0 — chalybeate/ferruginous

40,0—100.0 — strong chalybeate

over 100,0 — very strong chalybeate

Br- mg/l

25

Bromine

J- mg/l

3

Iodine

H2SiO3 mg/l

50

Siliceous

Rn ( n Κ/λ)

5

5—10 (14—55 Mache unit) —of very low radon

20-40 (55-110 Mache unit) — of low radon

40,-200,0 - (110-550 Mache unit) - of low radon

over 200,0 (over 550 Mache unit) of high radon

πΝ

—

below 3,5 — highly acidic

3,5—5,5 — acidic

5,5—6,5 — subacidic

6,8—7,2 — neutral

7,2—8,5 — mildly alkaline / alkalescent

over 8,5 — alkaline

Temperature

(ξΡ)

—

4—20°Ρ — cold

20—35— warm (low thermal)

35—42— hot (thermal)

over 42 — very hot (highly thermal)

Selected bibliography

Monographs and brochures

Foundations of national water legislation for water quality regulation in Central Asian countries. Part 1: Kyrgyz Republic, Republic of Tajikistan [in Russian] (2011) 

Foundations of national water legislation for water quality regulation in Central Asian countries. Part 2: Republic of Kazakhstan, Turkmenistan [in Russian] (2011) 

Foundations of national water legislation for water quality regulation in Central Asian countries. Part 3: Republic of Uzbekistan [in Russian] (2011) 

Resources