WaterQual

Chemical water quality

 

Nutrients

Physical water quality

 

Biological problems

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Water pH measures the concentration of protons (H+) in water. High pH (>7) is basic, pH 7 is neutral, and low pH (<7 is acidic). Water pH can affect the solubility of some fertilizer salts and the efficacy of insecticides, fungicides, and growth regulators. In general (but not always), higher pH reduces solubility and activity of these materials. pH is different from alkalinity (buffering to pH change).

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Alkalinity of irrigation water is a generic measurement of the total concentration of dissolved bases in the water. These bases can include bicarbonates, carbonates, hydroxides, phosphates, ammonium, silicates, sulfides, borates, and arsenate. Under most conditions, the ions that have the greatest effect on alkalinity are bicarbonates. Alkalinity can be thought of as the 'dissolved lime content' of the water. High alkalinity means high buffering (resistence to a drop in pH), and tends to increase pH of a container substrate over time. High alkalinity water can be neutralized with an acid, or balanced with a fertilizer with most nitrogen in the ammonium (acid) form. With low alkalinity, pH of a hydroponic solution or container substrate can change easily, no acid should be injected, and a fertilizer high in nitrate nitrogen (basic) is needed.

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Electrical conductivity (EC, also known as conductivity or soluble salts) is a measure of the total concentration of ions dissolved in water. EC is a generic measurement, because it does not indicate the type or concentration of which specific ions are dissolved in water. In general, the higher the EC, the greater the concentration of dissolved salts, and the greater the potential risk for salt buildup when water is applied to a substrate or recirculated in a nutrient solution.

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Total dissolved solids (TDS) is a measure of the total concentration of ions dissolved in water. TDS is usually measured with an EC meter, and 1 mS/cm = approx. 600 ppm TDS. EC and TDS are generic measurements, because they do not indicate the type or concentration of which specific ions are dissolved in water. In general, the higher the EC or TDS, the greater the concentration of dissolved salts, and the greater the potential risk for salt buildup when water is applied to a substrate or recirculated in a nutrient solution.

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Hardness is a measure of waters ability to form scale in pipes, reduce efficacy and solubility of agrichemicals, or to leave spots on leaves. Like alkalinity, the units used to report hardness are often calcium carbonate equivalents (CaCO3), but in this tool we calculate hardness by simply adding ppm of elemental Ca and ppm Mg. Whereas while alkalinity is a measure of all chemical bases in the water (bicarbonates and carbonates), hardness is a measure of the combined concentration of calcium and magnesium in the water because it is insoluble salts of ions, such as calcium carbonate, that form scale. A water softener may be used to remove hardness by replacing calcium and magnesium ions with an ion that doesnt cause scale, typically potassium. With hardness removal, the carbonates and bicarbonates remain in the water, but are changed from calcium and magnesium bicarbonate to more soluble sodium or potassium bicarbonate. Other treatments include reverse osmosis to remove Ca and Mg, and/or acid injection to increase their solubility and reduce precipitation.

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SAR is calculated from the balance of sodium to calcium and magnesium. With high SAR, the sodium in the water displaces the calcium and magnesium in the soil and results in a loss of soil structure and air porosity.

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N is a fertilizer nutrient. As nitrogen concentration increases, the fertilizer value is increasingly beneficial to crop growth and applied fertilizer can be adjusted downwards.

However, nitrogen rich run off can cause eutrophication in natural water bodies, especially above 10 mg/L.

Therefore, if the N level in water running off the property is above 10 mg/L or other minimum regulated level some remediation is advised such as constructed wetlands.

If N is in the nitrate form, levels of 10 mg/L N or above can also be harmful as a drinking water source.

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Cu is a fertilizer micronutrient. If high levels (0.3 ppm or above) of iron are present, then additional fertilizer Cu may need to be reduced. May cause toxicity in crop plants, and decreased rooting. Water treatments that oxidize ions can cause them to precipitate and be removed from the water. Treatments include aeration and settling in ponds, or chemical oxidation with chlorine, ozone or potassium permanganate followed by sand filtration.

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Phosphorus is a fertilizer nutrient. However, runoff of P to surface water bodies can cause algal blooms followed by a decrease in dissolved oxygen, killing aquatic animal life, and impacting drinking water quality. Levels above 0.1 mg/L in runoff increase risk of eutrophication.

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B is a fertilizer micronutrient. If boron is naturally present in irrigation water at 0.5 ppm, then B can usually be eliminated from water-soluble fertilizer. At 1 ppm or higher, B can cause toxicity in sensitive plants, for example leaf tip burn on monocots.

Boron is not effectively removed with reverse osmosis purification. To compensate for extremely high boron levels in irrigation water (>1.0 ppm), keep the substrate-pH above 6.0 and use calcium-based fertilizers, or blend with a more pure water source.

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K is a fertilizer nutrient. Increased K can limit plant uptake of other required nutrients such as calcium.

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Mo is a fertilizer micronutrient. Plants only require a very small amount, but deficiencies can occasionally occur in crops such as poinsettia. High levels are unlikely to cause an issue.

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Ca is a fertilizer nutrient. High levels of Ca are not particularly detrimental to plant growth, except that they may be associated with high salt or alkalinity levels in the water or a lack of balance with Mg. Low levels of Ca in the water can be supplemented with the addition of calcium nitrate- based fertilizers. High Ca may lead to scale and clogging of emitters, resulting in a need to acidify irrigation water.

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Si is a beneficial nutrient for plant growth.

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Mg is a fertilizer nutrient. High Mg levels are generally not a problem so long as they are in the proper ratio with Ca. However, high levels of Mg can be an indication of high salt or alkalinity levels in the water, and may contribute to scale and clogging of emitters. Low Mg levels in the water can be supplemented with the addition of Mg-based fertilizers.

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Ni is an essential micronutrient, but deficiency is only possible in a few crop plants including pecan.

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Sulfuric acid is frequently used for alkalinity control, and therefore in areas of the country with high alkalinity, high S level as sulfate is common following acidification. High sulfate-S may also occur in directly in water. High levels of sulfate-S in irrigation water will increase water EC, and may interfere with Ca uptake under certain situations. Sulfate differs from sulfite, which can occur in groundwater with low oxygen that is recognized by its 'rotten egg' odor. In contrast to sulfate, if irrigation water contains more than 0.1 ppm of total sulfides, sulfur bacteria may grow within the irrigation system, forming slime that clogs filters and emitters. To minimize sulfur bacteria issues from sulfite, either ensure there is no air-water contact until water is discharged from the system, or aerate water and convert to sulfate-S before use.

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Na and Cl in irrigation water increases dissolved salt level. High Na levels can cause a degradation in substrate-physical properties over time, particularly in substrate containing field soil.

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Fe is a fertilizer micronutrient. If high levels (0.3 ppm or above) of iron are present, then additional fertilizer Fe may need to be reduced. May form chemical precipitates (solid particles) that clog irrigation emitters. High levels of these nutrients can also favor slime-forming bacteria that clog filters and emitters. Water treatments that oxidize ions can cause them to precipitate and be removed from the water. Treatments include aeration and settling in ponds, or chemical oxidation with chlorine, ozone or potassium permanganate followed by sand filtration.

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Na and Cl in irrigation water increases dissolved salt level. High Na levels can cause a degradation in substrate-physical properties over time, particularly in substrate containing field soil.

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Mn is a fertilizer micronutrient. If high levels (0.3 ppm or above) of iron are present, then additional fertilizer Mn may need to be reduced. May form chemical precipitates (solid particles) that clog irrigation emitters. High levels of these nutrients can also favor slime-forming bacteria that clog filters and emitters. Water treatments that oxidize ions can cause them to precipitate and be removed from the water. Treatments include aeration and settling in ponds, or chemical oxidation with chlorine, ozone or potassium permanganate followed by sand filtration.

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F is added to many municipal water sources for human health, but can cause toxicity symptoms in some crops, for example monocots. Fluoride can be removed from water with activated carbon filters, or sensitive crops can be protected by keeping the substrate-pH above 6.0 and using calcium-based fertilizers.

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Zn is a fertilizer micronutrient. If high levels (0.5 ppm or above) of iron are present, then additional fertilizer Zn may need to be reduced. May cause toxicity in crop plants. Water treatments that oxidize ions can cause them to precipitate and be removed from the water. Treatments include aeration and settling in ponds, or chemical oxidation with chlorine, ozone or potassium permanganate followed by sand filtration.

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Total Suspended Solids, or TSS, is the concentration (in milligrams/liter or mg/L) of all particulate matter contained in a water sample, and includes fine particles of peat, silt, clay, microbes and other materials. To measure TSS, a water sample is filtered through a very fine screen, which is then dried and weighed. Suspended solids indicate the clogging potential in micro-irrigation lines.

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Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye. In drinking water, the higher the turbidity level, the higher the risk that people may develop gastrointestinal diseases. In irrigation water, high turbidity means high total suspended solids.

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Total colony count (expressed as CFUs, or colony forming units) of bacteria is a non-specific measurement, meaning the test estimates the amount of large groups of diverse organisms. Total CFU/mL of bacteria is not a good indicator of plant pathogens, because most microorganisms in water samples are likely to be beneficial or benign, rather than pathogenic. However, the risk of clogging of irrigation equipment increases when there is a high microbial density in water.

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Thermotolerant coliforms are a class of micro-organisms commonly used as bacterial indicators of sanitary quality of drinking water. Thermotolerant coliform testing is a term used to describe the method for assessing the presence and quantity of thermotolerant coliform bacteria in drinking water and other substances consumed by humans. Thermotolerant coliforms such as E.coli are present in higher numbers than individual types of pathogenic bacteria and their concentrations can be assessed relatively easily. Water with a high thermotolerant coliform level has a high probability of contamination by protozoa, viruses and bacteria that may be pathogenic. Two general types of analyses available for the enumeration of thermotolerant coliforms: Most Probable Number (MPN) Index, expressed as the number of thermotolerant coliforms per 100 mL of sample; Membrane Filtration (MF), expressed as colony numbers per 100 ml of sample.