An air grid for supplying air under pressure. The air grid may be used as an air scour system for a filter for removing at least some impurities (e.g., foreign matter of any nature including a solid, a liquid or a gas) from water or wastewater or as an aerator for aerating wastewater in an aeration tank or basin. The air grid includes an adapter for permitting in field adjustment of one or more components (e.g., drop pipe) of the air grid. Preferably, the adapter houses a portion of an air supply header and a portion of a drop pipe such that the air supply header is disposed above the drop pipe. The adapter may include a detachable sealing assembly. A tool may be provided for inserting and/or removing one or more components of the air grid from the operation environment.