What are common symptoms of tap water poisoning?

Mental status change: This is a rare condition that present with changes is mental status such as personality and behavior, headache, confusion, irritability and drowsiness, or muscle weakness. It can progress to seizures and coma. These symptoms are the result of brain swelling and electrolyte (sodium and potassium) imbalance. Drugs (ecstasy) and excessive water during excessive exercise are some causes.

Depends on type: Dr. Lawrence's answer applies to excessive water intake. As for "poisoning" it depends on the poison; the most common toxin in water is lead; this occurs gradually over time. Lead poisoning can cause headaches,fatigue,dementia etc. See https://tinyurl.com/yapcrqwt Much (but not all) tap water has fluoride. See https://www.honeycolony.com/article/fluoride-toxicity/ I advise purifying tap water.