# Chapter 2:4 Groundwater Groundwater is water in the saturated zone of earth materials under pressure greater than atmospheric, i.e. positive pressure. Remember that in the soil profile water is held at a negative pressure due to the attraction between negatively charged clay particles and water. The groundwater table is the depth at which the pressure between water and the surrounding soil matrix is equal to atmospheric pressure. Water enters groundwater storage primarily by infiltration/percolation, although recharge by seepage from surface water bodies may occur. Water leaves groundwater storage primarily by discharge into rivers or lakes, but it is also possible for water to move upward from the water table into the capillary fringe, a zone above the groundwater table that is saturated. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://swatplus.gitbook.io/io-docs/theoretical-documentation/section-2-hydrology/chapter-2-4-groundwater.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.