[1] While irrigation return flows are point sources, in the United States they are expressly exempted from discharge permit requirements under the Clean Water Act.
[2] Return flows generally return to the irrigation centre after a period of about three to four weeks; due to this, the farmers usually need to pour bleach into the water to clean it of any organisms that have entered the stream.
The return flows in irrigation is nearly 50% of the water supplied in silty clay soil type in tropical countries.
Rest of the water supplied to irrigation evaporates to atmosphere due to evapotranspiration.
When ground water is used in excess of recharge from rainfall/precipitation, the quality of groundwater deteriorates over a period of time and becomes unfit for irrigation use.