Diabetes is a metabolic disorder that happens either because the body either produces insufficient amounts of insulin or doesn’t use insulin properly causing blood sugar (glucose) levels to rise (hyperglycemia).
Drinking water before a fasting blood sugar test can actually decrease blood sugar levels, or at least prevent levels from getting too high.
Water allows more glucose to be flushed out of the blood. When you’re dehydrated, it means your overall blood volume is lower than normal, but your sugars will be the same. This means your blood is more concentrated (not diluted with water) and your blood sugar levels will be higher.
What Is Fasting Blood Sugar?
Measurement of fasting blood sugar (glucose) levels is used to check for diabetes. A fasting blood test requires a person to not eat or drink anything (other than water) for at least 8 hours prior to the test.
What Is Normal Fasting Blood Sugar?
Fasting blood sugar is usually measured in the morning, before eating anything for breakfast. Fasting blood sugar ranges are noted in the table below.
| Blood Sugar Level | mg/dL |
|---|---|
| Normal | less than 100 mg/dL |
| Prediabetes | 100 mg/dL to 125 mg/dL |
| Diabetes | 126 mg/dL or higher |
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https://www.diabetesdaily.com/blog/2011/02/how-water-impacts-blood-sugars/