Drinking up to 8 glasses of water per day can help keep your blood sugar lowered but if you're not already hydrated and your blood sugar is high then just drinking a glass of water will not lower the blood sugar levels.
Being dehydrated though can cause your blood sugar levels to rise so it's important to stay well hydrated with at least 8 glasses of water per day.
Also if your blood sugar is high then taking a tablespoon or two of apple cider vinegar can lower the blood sugar levels and can also lower blood pressure as well.
Eating plenty of fiber based foods and eating leafy green foods can also keep blood sugar levels in check and even help lower the blood sugar levels.