Chemical Property

Quality class of surface water and its classification

Specified by norm

I.

II.

III.

IV.

V.

unpolluted

slightly polluted

polluted

heavily polluted

very heavily polluted

norm

N-NH₃

<0.3

<0.7

<2.0

<4.0

>4.0

ISO 11732

N-NO₃

<3

<6

<10

<13

>13

EN 757453

${\text{P-PO}}_4^{3-}$

<0.05

<0.15

<0.4

<1.0

>1.0

EN 1189

Cl⁻

<100

<200

<300

<450

>450

ISO 6058

${\text{SO}}_4^{2-}$

<80

<150

<250

<400

>400

ISO 9280

Ca²⁺

<150

<200

<300

<400

>400

ISO 6058

Mg²⁺

<50

<100

<200

<300

>300

ISO 6059

E.C.

<40

<70

<110

<160

>160

EN 27885