Order to achieve the best possible Water Although treatment processes can sig cantly reduce the amount of contamination present in raw water, the costs and potential risks from residual amounts contaminants may be too high. This maining risk will become more of an the number of regulated contaminants increases and the level ofrisk that public is willing to accept decreases me water systems may require additional steps in the treatment train, such aeration or granular activated carbon ration, at greatly increased cost, The cacy of these treatment proces ally measured by the percentage of tamination they are capable ofremov. from the raw water, not necessarily the absolute contaminant level they in. Thus, even with the addition se treatment steps, the risks ronic or acute disease from the con- minants remaining in the finished ter may still be greater than the con- mer is willing to accept Allowing deg ation of a water source becau sence of or the ability to construct ter treatment plant, therefore, will not ximize protection of public health The Portland (Ore) Water Bureau re- tly completed a study for the AWWA search Foundation on watershed man- tment. The purpose of the study was