Employee was standing on the concrete at the wash plant spraying off the concrete pad with a water hose. The pad had some fine silt on it. EE said EE turned right and EE's left foot slipped out from under EE. Reported EE's fall to foreman and continued to work for the next 2 days. On 3/11/2016 EE came to work that morning and said EE went to ER.