Division of Agricultural Sciences and Natural Resources • Oklahoma State University
F-2401
Oklahoma Cooperative Extension Fact Sheets
are also available on our website at:
http://www.osuextra.com
Gordon Johnson
Extension Soils Specialist
Hailin Zhang
Director, Soil, Water and Forage Analytical Lab
All irrigation waters contain some dissolved salts. Dis-
solved salts are present because some chemical elements have
a strong attraction for water and a relatively weak attraction for
other elements. Two such chemical elements, for example, are
sodium and chloride. The amounts of these elements contained
in water must be very high before sodium will combine with
chloride to form the solid material sodium chloride, common
table salt. The total amount and kinds of salts determine the
suitability of the water for irrigation use. Water from some
sources may contain so much salt that it is unsuitable for
irrigation because of potential danger to the soil or crops.
Irrigation water quality can best be determined by chemical
laboratory analysis.
The Oklahoma State University Water Testing Laboratory
has developed chemical procedures for determining water
quality. This laboratory is part of the Soil, Water, and Forage
Analytical Laboratory provided through the Oklahoma Coopera-
tive Extension Service. Test results, their interpretation, and a
general recommendation on suitability of the water for irrigation
use are reported.
Measurements of Water Quality
The two most important measures for determining irrigation
water quality are:
1. The total amount of dissolved salts in the water.
2. The amount of sodium (Na) in the water compared to calcium
(Ca) plus magnesium (Mg).
The total dissolved salt content is estimated by measuring
how well the water conducts electricity. Salty water is a good
conductor of electricity. Electrical Conductivity (EC) is mea-
sured in units of micromhos/cm (µmhoms/cm). The ppm salt
concentration of the water is estimated ty multiplying 0.65
times the EC value. For example, water having an electrical
co