The use of hard water in spray preparations is very common in some parts of Australia. At Eureka! we expend a lot of effort ensuring that new products we develop for the Australian market are able to cope with hard water.
Hardness is caused by calcium and magnesium ions that are dissolved in the water. They get there when the water passes through rocks or soil that contain these ions, such as limestone. A lot of Australia’s farming land sits on such deposits and, not surprisingly, Australia have a lot of farms that have bores or even dams filled with hard water.
Tung Le one of Eureka!’s product development chemists explained that, “hard water can damage agricultural products in a number of ways. The three most vulnerable formulation types are; wettable granule, emulsifiable concentrates and those soluble liquids where the active ingredient is a salt”.
Granules
Dispersible or wettable granules are usually made up from powders. This type of product needs to wet quickly when added to water. Once wet, the granules must break back down to the powder form and disperse rapidly and evenly throughout all the water in the tank. Ms Le explained that, “most of this work is done by wetters and dispersants that are impregnated into the granules.” These dispersants either rapidly dissolve leaving the granules honeycombed with holes (which fill with water) or swell up breaking the granule apart until the original powder is reformed. Many granules have more than one type of dispersant as they often work better in combinations.
“The charged ions in hard water can interact with the granules’ dispersants, reducing their effectiveness. This stops the granules from breaking up completely,” said Ms Le. “These granule fragments need more energy to keep them suspended and so usually sink to the bottom of the tank. If they enter a pump intake they will block filters and nozzles. If they don’t cause blockages they cause uneven application and reduce the product’s efficacy.”
Emulsifiable Concentrates
When an emulsifiable concentrate is added to the water in a spray tank it forms small droplets of the oily EC components that suspend in the water. Usually the droplets are made up of the active ingredient dissolved in an oily solvent which is surrounded by a protective layer of emulsifiers.
Hard water reduces the performance of the emulsifiers causing droplets to join together forming larger and larger droplets. An emulsion with large droplets looks ‘grainy’. If the droplets continue to get larger the water and oily components will separate. Usually the oil is lighter than the water and floats on the surface as happens with the cream in milk.
Anionic emulsifiers are the traditional work horse of emulsion chemistry but their efficiency is easily reduced by hard water. By comparison, non-ionic emulsifiers are less affected by hard water and provide ‘steric repulsion’ which makes the droplets repel each other and this prevents them from joining together.
Figure 1. Our Stepan spray tank simulator is a critical piece of equipment that allows our chemists to actually witness interactions that happen between products in a spray rig. The simulator can be configured to imitate the sprayer conditions relevant to the products being test
Ms Le explained that, “the ions in hard water interact with the surfactants reducing their effectiveness and destroying the emulsion.”
Active Ingredient Salts
Many active ingredients are manufactured as acids. However, it is common for this acid form to be poorly soluble in water, less efficacious or both. A number of key products such as; glyphosate, 2,4-D and MCPA, start out as acids but are converted to salts to improve either their solubility in water or their efficacy. When dissolved in water in a spray tank these salts form positive and negatively charged ions. Ms Le said that, “in hard water these active ingredient ions mingle closely with huge numbers of the ions from the hard water. If the ions from the active ingredient react with those of the hard water they can form a new salt. Should this new salt be poorly soluble in water then it will precipitate, form a powder like substance and sink to the bottom of the tank.” Once again efficacy is lost and blockages are likely.
In some cases the new salt formed in hard water is still soluble enough to survive in the spay tank but reduces efficacy when it gets to the plant or soil surface. Glyphosate is a good example of this as it can form calcium salt in hard water. This less soluble form of salt reduces glyphosate uptake through leaves the leaf and can severely depress efficacy.
Protecting against hard water
In short, hard water is not good for agricultural sprays. However, for many it is the only water they have. Eureka! will continue to develop products that are better in hard water but sometimes it is not possible to solve the problem completely. Fortunately, there are products that can help overcome the effects of hard water in some circumstances.
Chelating agents such as EDTA can mop up the hard water before the agchem product is added to the tank but often the concentration of hard water is too high for this to be cost effective.
Ammonium sulphate is legendary for its benefit to glyphosate in hard water. It mainly works by releasing a large concentration of ammonium ions into the tank. The glyphosate is then more likely to bind with these ammonium ions than the calcium ions. Ammonium glyphosate is very soluble and is more quickly absorbed into the plant. There is even evidence to suggest that ammonium glyphosate moves through the plant more effectively than some other forms.
If you have products that need to be improved when used with hard water or tested for hard water tolerance please Anthony Flynn