An apparatus for promoting the efficient use of gases dissolved in a liquid by limiting the amount of off-gassing or evaporation from the liquid. The apparatus is a distribution/retention plate, may be utilized in a portable food washing system. The food washing system is a portable unit having a treatment chamber with an access door for the placement of food products on a loading plate. A food product is placed in the chamber and sprayed with ozonated water containing diffuse concentrations of ozone which reacts with and destroys organic contaminants on the food product. The distribution/retention plate is located at the bottom of the treatment chamber, and divides the treatment chamber from a reservoir and controls the rate of ozone off-gassing from the reservoir, thereby increasing ozone concentration in the water in the reservoir. In an alternative embodiment, the distribution/retention plate is utilized in an automatic dishwashing system.