It’s no secret: water quality can affect many herbicides, and glyphosate is no exception. Good, clean water is very important to maximizing the performance of Roundup WeatherMAX® and Roundup Transorb® HC. poor performance in Roundup brand agricultural herbicides due to poor spray water quality is entirely preventable.

Water quality parameters

Water suitability for herbicide application is defined by a few parameters, such as:

  • Conductivity – a physical measure of salinity. Conductivity is also a measure of total dissolved solids (TDS). A High TDS level raises the risk of precipitates forming.
  • Bicarbonates – a measure of the levels of bicarbonates in the water. Bicarbonates can reduce the effectiveness of ‘dim’ herbicides in group 1 (like sethoxydim, clethodim, and tralkoxydim) and 2,4-D.
  • Cleanliness or mineral content – water containing high levels of suspended silt or organic matter. These particles can bind with herbicides like glyphosate and diquat, reducing their effectiveness.
  • Iron content – iron (Fe) can bind with glyphosate, and can also react with oxygen to produce crystals, which could plug spray screens and nozzles.
  • Hardness – the sum of positively charged ions (cations), most often being calcium (Ca), magnesium (Mg), iron (Fe), and sometimes manganese (Mn) and zinc (Zn). Glyphosate binds easily (and tightly) to cations, reducing the effectiveness of the herbicide.

The factors that farmers should use to determine suitability of spray water for use with glyphosate is Conductivity, Cleanliness, and Hardness. Here are some spray water guidelines to determine suitability for use with Roundup WeatherMAX® and Roundup Transorb® HC herbicides:


  • Units: μS/cm
  • Glyphosate guideline: <500


  • Units: Visual assessment
  • Glyphosate guideline: Water should be free from suspended particles or organic matter. A slight yellow/green tinge is not expected to cause issues.


  • Roundup rate: 0.33L/ac – 0.67L/ac
    • A water volume of 5 GPA has a hardness limit of 700 ppm
    • A water volume of 10 GPA has a hardness limit of 350 ppm
    • A water volume of >10GP is not recommended for hard water
  • Roundup rate: >0.67L/ac
    • A water volume of 5 GPA has a hardness limit of 700 ppm
    • A water volume of 10 GPA has a hardness limit of 700 ppm
    • A water volume of >10GP has a hardness limit of 350 ppm

How can you manage poor spray water quality?

The first step in managing water quality is to test the source of your spray water, particularly if you are using well or dugout water. If the results indicate the water does not meet the guidelines, your first strategy should be to find another source.

If finding another source is impossible, or if your results are hovering around the recommended levels, there are a few proactive steps you can take to improve the performance of your Roundup brand agricultural herbicide with hard water:

  • Use the maximum recommended rate of Roundup brand agricultural herbicide for the weeds you are targeting.
  • Ammonium sulphate (AMS) can be added to water to help soften it. AMS comes in two forms, liquid (8-0-0-9) and dry (21-0-0-24).
  • Dry AMS (21-0-0-24) added at 2% weight/weight – 2 kg of dry AMS for every 100 L water.
  • Liquid AMS (8-0-0-9) added at 1% volume/volume – 1 L of liquid AMS for every 100 L water.

In dirty water, soil particles can tie up glyphosate, resulting in decreased control. Use clean water where possible. If soil particles or organic matter is suspended in the water source, try to filter the water prior to using it with Roundup WeatherMAX® and Roundup Transorb® HC.


As a rule of thumb, any water that tests over 700 ppm hardness should not be used with glyphosate, regardless of water volume or spray rate.

The first step to managing spray water is to test your water. If it falls below the recommended guidelines, you can rest easy using that source. If your water is above the recommended guidelines and is considered poor quality, implement the proactive steps mentioned above. Spray water quality is a management issue within your control.

Remember to always read and follow pesticide label directions.