2. the drinking water does not contain—
(a)concentrations or values of any of the parameters listed in Tables A to D in Part II of this Schedule in excess of the prescribed concentrations or values;
(b)concentrations of trihalomethanes (being the aggregate of the concentrations of trichloromethane, dichlorobromomethane, dibromochloromethane and tribromomethane) in excess of 100 μg/l;