The efficiency of well-screen performance varies considerably depending on the physical characteristics of the aquifer and gravel pack, the open area of the screen, and the quality of the source water. If an aquifer consists of only gravel the size of golf balls, then slot type matters little. With such a mixture of grain sizes, perforated pipe would likely pump sand, and the width of other slot types must be adjusted to limit the sand that passes. To serve these purposes, the screen should have the largest possible open area consistent with strength requirements. The quality of the water source may also effect screen efficiency over time.
Corrosive water can open a properly sized slot over time to the point of pumping sand.
Water high in dissolved solids can precipitate a mineral scale when pressure changes occur. This scale can plug the slots and restrict flow. Air entrapment in the aquifer may occur if the pumping water level enters a poorly designed screen zone, creating an environment conducive to bacteria growth and further plugging. Keeping good operations records will allow you to predict changes and minimize the impact of source water quality before it's a problem too great to remedy. Any of the aforementioned inefficiencies increase operating costs.