The quality of recycled water depends upon the source water and the level of treatment. Generally recycled water will have a higher concentration of dissolved salts than drinking water. Water with high levels of salts can have adverse effects on plant health and appearance; however, most recycled water produced does not have harmful levels of salts for most plants. Irrigation constituents of greatest concern to agricultural crops or ornamental species are chloride, sodium, bicarbonate, boron, and fluoride. Appropriate plant selection and good irrigation management can minimize the potential impacts of the salts or specific ions of concern.

There is a potential for salt accumulation when using recycled water. As a result, it may be necessary to slightly over-water or leach plants irrigated with recycled water. A general rule of thumb is to allow for a 10% over watering depending on soil type and plant characteristics. Well drained soils and rainwater will help mitigate salt accumulation effects.

Plants sensitive to salts may be affected mostly by tip burning when recycled water with high saline content is applied by spray leaving salts behind when the water evaporates. Drip irrigation rather than overhead irrigation will minimize foliar injury.  Studies have showed low occurrence of injury to many common landscape plants. Findings through other studies have showed health ratings were equal or higher using recycled water over potable water in all species tested. In some cases, nutrient rich recycled water can be beneficial to plant growth and might reduce the need for additional fertilizers.

Turf grasses, most annuals, and deciduous trees are more tolerant of saline water than evergreens. Turf grasses either have built in tolerance of saline conditions or do not accumulate high levels of salt because of frequent mowing. Deciduous plants don’t accumulate salts in plant tissues because they shed their leaves each fall.

There is a website, Salinity Management Guide, which is full of informative resources including a 320-page report on salt management with recycled water for Coastal California.