Greywater, household wastewater excluding toilet waste, is a source of water and nutrients for gardens. However the challenge in greywater reuse is that it also contains

• detergents, soaps and chemicals, which may require treatment,
• human pathogens, i.e. microorganisms which can cause illness.

Therefore for soil health and food safety, certain precautions are needed:

• Greywater should be used with great caution or not used at all especially on plants that are eaten raw.
• Greywater reuse can be made safer by greywater treatment and by underground irrigation or at least spreading the water by drip irrigation under a layer of mulch. Application of greywater, even treated greywater, may be restricted for a number of weeks prior to harvest.
• Groundwater recharge makes use of the soil's natural filtering ability, and microorganisms which break down compounds and pathogens, as well as adding to groundwater levels. It also increases water availability without needing to apply greywater close to edible plants.
• A relatively safe place to use this resource is where the greywater irrigation occurs below a thick layer of mulch, and edible parts of the plant are well above the ground - fruit trees or vines on trellises, for example.