A key basic assumption in the development of any semiconfined artesian aquifer as a source of feedwater is that the quality of the water will change with time. The issue to be resolved is how to develop the water supply to minimize the rate of change. This paper discusses the development of carbonate aquifers in South Florida and the development of siliciclastic aquifers of the Eastern Coastal Plain. A major conclusion that can be drawn from this discussion is that if the groundwater system is not well understood at a given site, the design of the wellfield should be very conservative. This means increasing production well spacing and increasing the number of production wells to effectively decrease individual well yields. As additional data are obtained, changes can be made to the wellfield design to reduce costs.