Application rate is how much effluent a square foot of a specific site’s soil can safely absorb per day, measured through a percolation test or a fuller soil evaluation. It is the number that converts a house’s design flow into an actual drainfield size: divide the required daily flow by the application rate, and the result is the field area needed.
Application rate is not a property of “soil in general” or of a region; it is measured on the specific site, because soil texture, structure, and layering can vary meaningfully even across one lot. That is why a percolation test or soil evaluation is required at the time of design rather than assumed from a typical or regional value.
Coarser, more open soils generally support a higher application rate (they can absorb more per square foot per day), allowing a smaller field for the same design flow. Tighter, clay-heavy or poorly structured soils support a lower rate, requiring more field area, and very low rates can push a design toward an alternative dispersal method that uses the available soil more efficiently, or toward pretreatment that reduces the loading the soil has to handle.
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How much effluent a square foot of the site's specific soil can safely absorb per day, used to calculate the required drainfield area.
Soil texture and structure can vary meaningfully even within one lot, so a measured, site-specific rate from a percolation test or soil evaluation is required rather than an assumed typical value.
Required field area equals the design flow divided by the application rate, so a lower rate (slower-absorbing soil) requires a larger field for the same house.
Guide last reviewed 2026-08-31.