It is possible to have too much of a good thing. It turns out that water, the liquid that keeps you alive, can also poison you.
One poor woman in the UK found out the hard way when she started noticing symptoms of a UTI, and thought she could "flush it out" of her system. Pro tip: This is why doctors exist, so you don't have to DIY a treatment plan. She started drinking more than a cup of water every 30 minutes to treat the urinary tract infection, but ended up hospitalized. Talk about a backfire.
The patient had dangerously low levels of salt in her blood, a condition called hyponatremia, more commonly known as water intoxication. This happens when people drink so much water, it dilutes their blood of important nutrients like salt and electrolytes. It can create swelling of brain cells, and symptoms include disorientation, headaches, nausea, and vomiting. If sodium levels dip too low, it can even lead to death -- much more serious than a UTI, medically speaking.
As the woman's condition progressed in the hospital, she vomited a few times and had difficulty speaking. Her sodium level was at 123 millimoles per liter, and anything below 125 mmol/L is considered deadly. Luckily, doctors reduced her fluid intake and she was released from the hospital the following day.