No, Augmentin (amoxicillin/clavulanic acid) antibiotic suspensions should not be mixed with more water than indicated on the drug label.
Antibiotic powders for suspension have a specific amount of water that need to be added to them in order to attain the correctly labeled concentration. For example, the 100 ml bottle of Augmentin 200 mg/5 ml needs to have 95 ml of water added to the powder in order to attain the labeled concentration. If more water is added, the product will be diluted, resulting in a lower than intended concentration. This has the potential to cause therapeutic failure due to under-dosing.
Below is a chart for common strengths of Augmentin and how much water needs to be added to attain the correct concentration:
It should be noted that the pharmacist should be adding water to your antibiotic powder as they use calibrated measuring devices with purified water.