This option requires a similar level of treatment as traditional wastewater prior to discharge into receiving bodies of water. The technology involved is simply a second set of water pipes that carry treated wastewater back to large-volume irrigators. Golf courses, office parks and city gardens that typically use clean drinking water for irrigation can switch to treated wastewater without measurable ill effects (Baumann and Dworkin, 1978).
While it is possible for all domestic irrigators to switch to recycled wastewater for their home irrigation, the cost of running new non-potable water lines to individual residences is thought to be prohibitive. Cities with non-potable reuse typically sell wastewater to a small number of large-volume users such as those previously mentioned. The benefits of non-potable reuse include minimizing the cost of drinking water treatment by decreasing the demand, and increasing the beauty of the community with a new source of irrigation water. Additionally, some recycled water infiltrates into the groundwater, helping to prevent the damage associated with falling groundwater tables (WRA, 2001).
One negative aspect of direct non-potable reuse is the accumulation of byproducts over time in the irrigated soil. If the recycled wastewater has a non-zero concentration of salts or other chemicals, those chemicals may accumulate over time where the water is applied. Usually physical and biological processes in the soil offset this concern, unless the concentration of a pollutant is unusually high(Baumann and Dworkin, 1978).
Another negative effect is the potential consumer confusion between potable and non-potable water piping. Mixing up potable and non-potable water pipes is a concern when users of recycled water include ordinary residences. Industrial users typically do not suffer such problems, but small children may drink from a home faucet that is intended solely for irrigation water. Because treated wastewater is not devoid of pathogens and harmful chemicals, the consequences of ingestion can be severe (NRC, 1998).