This methodology forces accountability by having clearly defined stages where activities are frozen and placed under change order control. Many people are not willing to take that responsibility. For the WaterSluice methodology to work it is necessary to create an environment where taking responsibility and accountability for a decision need not be fatal to the individual if the decision later leads to a failure. Otherwise, people will avoid accepting accountability leading to missed goals.
An attitude change towards testing is necessary by the teams since all teams are involved in testing from the beginning.
The WaterSluice methodology requires that people communicate well up front which is a difficult task since all four phases represent different perspectives.
The methodology trades off total flexibility with the reality of product delivery.