Reducing the allowable density of structures can be useful in protecting a sensitive ground water area since it lessens the potential impacts of development by reducing the total number of buildings, amounts of impervious surface, or numbers of septic systems within the zone. Since large-lot zoning tends to leave more open land, it can also help maintain natural vegetation and landscape contours which contribute to the filtration of runoff and recharge water. The down side of large lot zoning is that it uses more land and almost guarantees that private septic systems rather than a common waste water collection system will be used, in which case there would actually be more discharge to the ground than if densities were higher. If, however, there is no chance of a public sewer system, then larger lots would result in fewer septic systems and fewer failures than smaller lots.
Cluster zoning and planned unit developments (PUD) are another strategy to reduce densities near wellheads. These methods increase densities within portions of parcels while the remaining areas are left in open space, and that open space could be established to protect ground water. This technique offers flexibility in designing and locating development in wellhead protection areas so that the more sensitive portions of a site can remain in a natural unaffected state.