In enzymology, an alpha-glucan, water dikinase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are ATP, alpha-glucan, and H<sub>2</sub>O, whereas its 3 products are AMP, phospho-alpha-glucan, and phosphate.
This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing groups (phosphotransferases) with paired acceptors (dikinases). The systematic name of this enzyme class is ATP:alpha-glucan, water phosphotransferase. This enzyme is also called starch-related R1 protein, GWD.