Maltose is found in grains, when they soften and grow in water, and vegetables when starch is broken down for food. It is an intermediary in the digestive process. It consists of two molecules of glucose. If you add water to the solution it is diluted. This slows the process as enzymes are floating rather than rapidly meeting their target.
By diluting the solution with water, it makes it more difficult for the enzyme and substrate to find each other. (There is more space for them to have to float through to find each other - for example, say you lose your binder. It would be much easier to find your lost binder if you know you lost it in your bedroom vs. if you lost it at school because the school campus is much bigger than your bedroom.)