The water absorption index (WAI) and water solubility index (WSI) are parameters used to evaluate the functional behavior of native or modified starches. WAI measures the starch granules’ ability to absorb and retain water, while WSI reflects the release of soluble components such as glucose, maltose, and low-molecular-mass dextrins, as a result of physical and/or chemical starch modification treatments. For example, pre-gelatinized starches obtained by hot extrusion are evaluated for their WAI and WSI content to determine as processing conditions. These analyses aid in evaluating the technological performance of starches and their potential industrial applications, particularly as thickening agents in soups, creams, broths, and related products. This chapter also describes in detail the standardized experimental protocol for determining both indices.