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How do I dispose of wash water?

Check local laws as to how to dispose of wash water. For a small amount of wash water, you may be able to spray it over an unsprayed area of crop or an area of low environmental value. If no guidance exists, follow the steps below.​

Wash water without detergent or dirt

This may be wash water used to clean:

  • the inside of plastic/metal pesticide packs
  • the inside of mixing equipment
  • the inside of the sprayer tank.

Use this wash water (which is free of detergent or dirt) to dilute the pesticide product when mixing provided​:

  • the label states that the pesticide you are mixing can be diluted in water
  • the water was used to wash the inside of the same pesticide's packs, or to wash equipment used with the same pesticide.

Spray the final wash water (free of detergent or dirt) from cleaning the inside of your sprayer onto an un-sprayed area of your crop (for which the product has been approved). Otherwise,spread the diluted waste thinly over an area of uncropped, unused ground of low environmental value. Or consider making and using a bio-bed.

Wash water with detergent or dirt

Wash water with detergent or dirt (perhaps from washing your PPE or the outside of your sprayer) should not be sprayed over your crop. If allowed in your country, spread the wash water thinly over an area of uncropped, unused ground of low environmental value. Check the area is neither compacted nor prone to flooding. Do not use the same area more than once a year.

Check the rules in your country about bio-beds, and consider making a bio-bed for smaller amounts of wash water.

To make a basic bio-bed

  • Dig a pit in the ground where there is no risk to groundwater and more than 100 metres from surface water, wells or homes.
  • Fill the pit with a mix of straw, soil and compost. If you have sawdust, add a layer of this.
  • Turf over the pit.

Pour the wash water slowly into the biobed. Do not let the biobed overflow.

To make a better bio-bed

  • Make sure that the pit is 60 cm deep and 30 cm wide.
  • Line the bottom of the bio-bed with 5 cm of clay to contain the wash water.
  • Fill the hole with 25% of high organic soil, 25% vegetation/organic matter and 50% maize stubble to absorb any pesticide and encourage micro-biological breakdown.
  • Line the lip of the bed with 10 x 30 cm concrete blocks to contain the wash water as it is poured into the bed.
  • Cover the bed with a water-proof cover to keep excessive rain off the biobed.

Check local laws on how to dispose of larger amounts of pesticide wash water. The World Health Organisation (.pdf, page 164) recommends that wash water be collected in a marked drum with a tight lid and treated as toxic waste.