The air gap provides an air space between your tank’s water level and your municipal refill line to ensure that cross contamination and back-flow siphoning is impossible. In addition to air gaps, it is always suggested to use check valves, RPZ valves, and 3P Technik Filtersysteme BackFlow Traps. Air gapping is required by code in many areas when using a municipal water source to refill your water tank. Many people who harvest rainwater often just use a inlet basket on their poly tanks as the air gap. Although it is an air gap measure, we do not recommend leaf baskets as the only source for filtration of rainwater before it enters your system; refer to our filter products for more information and direction. In good system that uses inlet backfill water will also add a float switch to support their system.