Water policies and programs in the western United States have not always achieved the results originally envisioned. The surrounding circumstances, from public opinion and involvement to hydrology and administrative capacity, significantly influence policy and program effectiveness. This Article identifies and provides examples of these key external characteristics, categorizing them under five overarching factors: social and political dynamics; physical landscape; economics; law; and administrative capacity. Considering these factors, and tailoring water policies and programs accordingly, offers the best chance of achieving the desired results.