Interpreting WaterQuality Reports

Karen L. Panter, Ph.D., C.P.H.

Horticulture and Specialty Crops

Department of Plant Sciences

How do we measure water quality?

• Alkalinity• Salinity• pH• Sodium

Adsorption Ratio• Specific Ions• Suspended

Solids

Desirable Characteristics

• EC– <0.5 dS

• pH– 5.0 – 7.0

• Alkalinity– 40 – 100 ppm

• Nitrate– <5 ppm

• Magnesium– <24 ppm

• Ammonium– <5 ppm

• Phosphorus– <5 ppm

• Potassium– <10 ppm

• Calcium– <120 ppm

• Sulfates– < 240 ppm

Desirable Characteristics• Manganese

– <2 ppm• Iron

– <5 ppm • Boron

– <0.8 ppm • Copper

– <0.2 ppm • Zinc

– <5 ppm

• Molybdenum– <0.02 ppm

• Aluminum– <5 ppm

• Sodium– <50 ppm

• SAR– <4

• Chloride– <140 ppm

• Fluoride– <1 ppm

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Desirable Characteristics

pH• A pH reading is a

measurement of the hydrogen ion concentration of a solution– 0 most acid to 14

most basic– pH = 7 is neutral

• pH = 5.4 to 7.0 acceptable

[ ]pHH

= +

1

Salinity• Total dissolved

solids• Measured by

electrical conductivity– determined by

passing a current through the solution and determining its electrical conductance

– units are millimhos/cm, or

– decisiemens/meter (dS/m)

Salinity

• Restrictions to use:– < 0.25 dS/m None– 0.25-0.75 dS/m Moderate– 0.75-2.25 dS/m High– > 2.26 dS/m Severe

• Multiply by 700 to convert to ppm TDS– Total Dissolved Solids

Alkalinity

• The ability to neutralize acid (meq·L-1) or ppm (upper limits)– total carbonates (CO3 )– bicarbonates (HCO3 )– hardness (Ca + Mg)

• Restrictions to use (in meq·L-1):– < 2 None– 2-8.5 Slight to moderate– > 8.5 Severe

SAR - Sodium Adsorption Ratio

• Relates sodium to calcium and magnesium levels in water

• Must be done by water testing laboratory• Can lead to deficiencies in calcium and

magnesium

Sodium Adsorption Ratio• High sodium in relation

to calcium and magnesium can be detrimental to plant growth

• SAR should be < 10• Greenhouse < 4• Calcium may

precipitate

[ ][ ] [ ]

SARNa

Ca Mg=

+

+

+ +2 2

2

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Examples of Real Analyses

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And now….any questions?