Water has been included as a control of the experiment.
A vital part of most science experiments is the control. By definition, the control in a science experiment is a sample that remains the same throughout the experiment. The control must remain the same or equal at all times in order to receive accurate results. You can have as many controls as necessary to achieve results.
The negative control group in the starch and sugar experiments were distilled water. The dH20 group was not expected to have any sugar or starch in it. This negative control group ensures that there were no unexpected variables acting on the experiment to produce a false- positive.
The positive control group in the starch experiment was the starch sample, and the positive control group in the sugar experiment was the glucose sample. The positive control group ensures test validity – ensuring the experiment accurately tests known properties. - See more at CourseHero.com