In the case of water pollution, do you think the choice of pollution emission policy instrument (such as emission standards versus effluent charge) depends on whether the source of pollution emission is:

(a) a "point source" such as a sewage-outflow pipe, or

(b) a "non-point source" such as agricultural runoff, in the form of sediment and fertilizers, that is emptied into a large water body, for example a river? Hint: in attempting to answer this question think about transaction cost.