Hydraulic loading refers to the total amount of water applied to the soil. No matter how permeable the soil, the leaching potential remains low if there is insufficient water to move completely through the soil. Where rainfall exceeds both plant consumptive use and the soil's ability to store water, leaching occurs. Water moving below the root zone ultimately reaches groundwater, carrying with it soluble soil constituents. In these soils, the leaching potential is highly correlated with soil permeability.
Irrigation compensates for water deficits in dry areas.
Most irrigation water is taken up by plants, but some usually passes through the soil out of the root zone. Thus irrigation can increase groundwater vulnerability. Careful management of the amount and timing of irrigation water applications can be very effective in reducing the risk of groundwater contamination. The position of a soil in the landscape also influences its hydraulic loading. Soils near a hilltop often shed water, either by runoff over the surface or by lateral flow within the soil.