Answers below address issues ...

Answers below address issues of pathogenic aerosol from application methods, pathogenic contamination of edible portions of crops, and plant uptake of solubilized heavy metals--all of concern. One must also note that alkali conditions can damage soils in dry climates--most grey water contains high levels of salts , and over application can contaminate ground water sources--NO3-. 

However, grey water is a great source of irrigation water for many reasons: contains nutrients, source of water in drought, use reduces eutrophication of receiving waters...

Aeration helps to reduce pathogens, subsurface irrigation reduces chances of contaminating edible portion of plants (changing water sources 15 days prior to harvest is common), and source testing can identify heavy metal polluters. (e.g.  itai itai).

Hydroponic methodology can eliminate damaging soils with alkalinity or heavy watering during seasonal wet periods.

More care in using fresh water will reduce the issues encountered by recyclers.

Water-Energy-Food, the solution is obvious, reusing water.