Managing Spray Water Quality

What’s the purpose?

Using poor water when spraying can adversely impact the performance of many agricultural products. Such detriments include reduced solubility, chemical breakdown, reduced herbicidal activity, and even potential equipment defects (Altland, 2012; Fipps, 2003; Hansson & Mattsson, 2002). This can be particularly problematic as water often makes up at least 95% of a spray solution (Whitford et al., 2009). Ultimately, mismanagement will affect whole farm operations as target pests are not adequately controlled, which may lead to increased economic costs.

Where to start?

To maximise efficacy of most farm chemicals, water quality used for spray operations must be managed appropriately (Whitford et al., 2009). All producers should investigate for and collect accurate information regarding their water quality status to determine what chemicals are used and at what rates. Sending a water sample to a laboratory is a simple starting point, whilst consulting chemical labels and manufacturers will provide further clarification. At minimum, tests should look to measure total hardness, pH and salinity.

Total hardness

Total hardness is a measure of the number of cations or positive ions that are present in the water and is typically expressed in parts per million (ppm). These are most commonly related to calcium and magnesium bicarbonates, sulphates, chlorides and nitrates (da Cunha et al., 2020; Devkota & Johnson, 2020; Hoffman et al., 2008; Thelen et al., 1995). Put simply, the greater the concentration of these cations, the harder the water, whilst a reduced concentration indicates softer water. Negatively charged molecules that are present in weak acid herbicides (eg. glyphosate, 2,4-D, MCPA, diflufenican) are attracted to these positive charged ions, causing them to bind together, altering their properties and forming less readily absorbed salts. This ultimately reduces their activity on the target and diminishes overall weed control (Schortgen & Patton, 2020; Zollinger et al., 2011). Research has shown that hardness further influences the droplet size spectrum of a spray and can reduce droplet surface tension, leading to an inefficient and variable application (Hoffmann et al., 2008). To bolster analysis, producers may look to separate total hardness and bicarbonates, as these are not detected in most standard tests. Limestone areas would benefit from this as they are significantly prone to high levels of bicarbonates. In conclusion, common practice is to treat water that is above 250ppm. Refer to Table 1 for hard water boundaries.

Table 1; Classification of hard water as provided by the NSW Department of Primary Industries (McDougall, 2012).

Water Classification Parts per Million (ppm)
Soft <50
Moderately Soft 50 – 75
Moderately Hard 75 – 150
Hard 150 – 300
Very Hard >300

Water pH

The pH value is a measure of the concentration of hydrogen ions (H+) present, and largely determines the acidity or alkalinity of a solution. A 1 to 14 scale is typically used, where 1 is acidic, 7 is neutral and 14 is alkaline. Alkaline water (pH > 8) and acidic water (pH < 5) can cause hydrolysis, increased chemical dissociation, poor droplet contact with the target, and often gelling and increased volatility of some products (Devkota & Johnson, 2020; Green & Hale, 2005; Deer & Beard, 2001). When water pH bypasses these preferred upper and lower boundaries, activity of active ingredients used in pesticides may be jeopardised, compromising overall performance. As a general rule, pesticides perform most efficiently in slightly acidic water, with a pH between 4 – 6. Best treatment for reducing pH is to incorporate a pH buffering agent, which will work to reduce the pH to a set point and leave it there.


Salinity’s impact on water quality and pesticide performance is often overlooked (Whitford et al., 2009). It is usually measured as the water’s electrical conductivity (EC). High levels of sodium can lead to the deactivation of some products, whilst also resulting in chemical precipitation out of the solution. Producers should be aware of sodium chloride concentration above 1000ppm or EC’s above 500 mS/cm. Easiest treatment is to dilute with fresh water (Fipps, 2003).

Dirty water

Silt, clay and organic matter suspended in the water are known to affect many products. Turbidity is a common term used to describe the clarity of a solution, and measures the amount of light scattered by material in the water (Whitford et al., 2009). An increased intensity of scattered light signifies high turbidity or an increased presence of material (Altland, 2012). Research has indicated that some products, such as glyphosate and paraquat, can bind to suspended material or colloids (Whitford et al,. 2009). This is highly problematic as the chemical becomes unavailable for plant uptake. Removal of these colloids is best achieved using lime or aluminium, which work to settle out the tank and shift these to the bottom.


Higher water temperatures can amplify chemical breakdown, whilst low temperatures may induce solubility issues or gelling (Devkota et al., 2016; Hansson & Mattsson, 2002). In addition, diluting wettable granules or powders will be more difficult in cold water. Constant tank agitation is the simplest amelioration.

Spraytec’s mission

At Spraytec, we understand the importance of managing water quality to ensure performance and efficacy is to the highest standard. As part of our mission, we regularly conduct on-farm, in-shop or at-meeting demonstrations using our own water testing kit. We use indicator strips that test total hardness and pH, providing a simple measurement of water quality which can inform producers quickly. We also note the need for simplified operations on-farm. To achieve this, we are working on our own patented products that aim to combat most water deficiency issues within one formulation. For further queries or to find a solution, please get hold of one of our team members.


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Deer, H. M., & Beard, R. (2001). Effect of water pH on the chemical stability of pesticides. AG/Pesticides14, 1.

Devkota, P., & Johnson, W. G. (2020). Efficacy of dicamba and glyphosate as influenced by carrier water pH and hardness. Weed Technology34(1), 101-106.

Devkota, P., Whitford, F., & Johnson, W. G. (2016). Influence of spray-solution temperature and holding duration on weed control with premixed glyphosate and dicamba formulation. Weed Technology30(1), 116-122.

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Hansson, D., & Mattsson, J. E. (2002). Effect of drop size, water flow, wetting agent and water temperature on hot-water weed control. Crop Protection21(9), 773-781.

Hoffmann, W. C., Bagley, W. E., Fritz, B. K., Lan, Y., & Martin, D. E. (2008). Effects of water hardness on spray droplet size under aerial application conditions. Applied Engineering in Agriculture24(1), 11-14.

McDougall. (2012). Water quality for chemical spraying. NSW Department of Primary Industries.

Schortgen, G. P., & Patton, A. J. (2020). Weed control by 2, 4-D dimethylamine depends on mixture water hardness and adjuvant inclusion but not spray solution storage time. Weed Technology34(1), 107-116.

Thelen, K. D., Jackson, E. P., & Penner, D. (1995). The basis for the hard-water antagonism of glyphosate activity. Weed Science43(4), 541-548.

Whitford, F., Penner, D., Johnson, B., Bledsoe, L., Wagoner, N., Garr, J., … & Blessing, A. (2009). The impact of water quality on pesticide performance: the little factors that make a big difference. PPP-86. West Lafayette, IN: Purdue University Extension.

Zollinger, R., Nalewaja, J., Peterson, D., & Young, B. (2011). Effect of hard water and ammonium sulfate on weak acid herbicide activity. In Pesticide Formulations and Delivery Systems, 30th Volume: Regulations and Innovation. ASTM International.