There are a wide variety of different well construction types. Many wells are completed as open-hole in rock formations. There are a number of different configurations for slots within a well screen to allow the water to pass through the screen material. The form or geometry of the opening in a well screen may also influence the likelihood of mechanical type losses due to blockage and the degree of difficulty in developing. Easier rehabilitation results from the absence of a well screen and/or gravel pack that often create additional barriers to easy and effective well development. In addition to the type of screen, the type and thickness of the gravel pack and the type of surrounding formation in which the well is completed are also important. A pump test is usually done to generate a baseline for well efficiency and specific capacity to be determined. Approach and entrance velocities are very important when designing wells.