Each year Mr A sells N mature animals and buys in N young animals. The animals are worth most when they are C years old. The net profit from each animal sold is U dollars.

Lately, however, because of a waterborne disease Mr A's profit has been reduced. He must make a decision in order to make more profits.

It is understood that the animals contract the disease only from drinking the water. They do not get it from each other. And every pathogen ingested has the same likelihood of causing death. The probability of any animal not dying from the disease during the C-year period before sale can be expressed as:

Q(X) = e*X where k = Constant and X = pathogen conc.

A manufacturer said that he has a treatment system that could eliminate the disease 100%. A unit for a herd of size N costs only V dollars. Discuss your findings and provide appropriate recommendations useful for the engineering community-with particular emphasis on water quality standards.