Ever since the industrialization of cheese production, whey has in large amounts been dumped into rivers, lakes or similar water reservoirs. However, as the whey contains organic substances, oxygen is required for the decomposition, and dumping of whey will therefore have a great influence on the environment. If the dumping is of such a quantity that the decomposition requires all the oxygen available in the water, all life will die followed by a putrefactive process. It is therefore obvious that the amount of whey which can be dumped per hour depends on the amount of oxygen available which is again determined by the amount of water per hour and its content of oxygen. It is therefore difficult to state exact amounts of whey which may be dumped. In some countries, Denmark for example, it is even forbidden to dump anything without a prerinse in a special cleaning plant. As a guide, the degree of organic impurities in waste water is expressed by the requirement for oxygen for biological decomposition in a 5 days' period, namely the so-called BOD5. Average waste water from households will have a BOD₅ of 300 mg oxygen per litre. With an average amount of 200 litres per person per day it corresponds to 60 g oxygen, also known as a person equivalent. For whey the BOD₅ is approx. 60 g oxygen/litre, i.e. 1 litre of whey corresponds to 1 person.

Instead of cleaning the whey in special cleaning plants some dairies have disposed of large quantities of whey by spray-irrigating it over the fields, which is an effective method giving benefit both to the factory and to the farmer. The amount of whey per hectare depends on the pasture and the rainfall. The irrigation is usually done in a cycle with 14 days between each doze, which means there should be plenty of land near the cheese factory (but at least 200 m from nearest habitation). The amount which can be sprayed is about 7 m³/ha/day.