As the name implies, in this kind of aerators, water flows down from height resulting in air-to-water contact. The different aerators falling in this range are:

• Spray Aerator: In spray aerator, spray nozzles, designed to provide specific water droplet size for the desired contact time, disperse the water into small droplets that creates a large surface area of water in contact with air. This facilitates the absorption of oxygen and expulsion of undesired volatile substances. Spray aerators are an efficient method of transfer of gases.
  
  
• Cascade Aerator: In cascade aerator, water fall down in a thin film over a series of steps or baffles. It can be rectangular or circular in shape. As the water falls down and turbulence is created, the exchange of gases takes place.
  
  
• Cone Aerator: Cone aerator is similar to cascade aerator but cone shaped. The water is pumped to the top cone and it cascades down the aerator. This type of aerator is generally used to oxidize dissolved iron and manganese to insoluble forms, which can then be removed by filtration.
  
  
• Tray Aerator: In this design, multiple trays are stacked one over other. Water to be aerated is distributed over the top tray. These types of aerator are either natural draft type or forced draft type.
  
  

In natural draft type tray aerator, the tray contains one or following mater material: coke, lime, rock, ceramic balls or other media. These materials provide additional surface contact area between air and water, and hence the efficiency is increased.