Yes, drinking too much water can have scary side effects. It is normally said that drinking 2 liters of water a day is enough for an adult. But the best thing is to drink as much as your body needs in a day. Drinking more than 2 liters of water everyday can have some usual side effects. It can cause hyponatremia which is the deficiency of sodium in the blood. Excessive drinking of water swells up your cells causing hyponatremia. You can also lose potassium in the blood and get affected by hypokalemia. Too much water can damage your glomeruli and put pressure on your heart function too. It can also affect your digestion.