According to Dr Google...
Over-hydration and water intoxication happens when you drink more water than the kidneys can get rid of via urine. Kidneys can eliminate about 5.3-7.4 gallons (20-28 liters) of water a day, but they can't get rid of more than 27-33 ounces (0.8-1.0 liters) per hour.
Ok, so say 2-3 liters in relatively short period of time.
We're around 60% water so a 83kg (183lb) person has around 50 liters. That'd be 4%-6%. I guess we'd call that a few percent.
Whereas there's probably not a lot of, say, cyanide in the average human. Like virtually none. So although only 3mg/L is typically fatal that would be a vast increase in concentration.
So maybe
@CalG is correct given the wording.
Don't know about everyone else but I reckon over 1 liter of water per hour is lot of water to 'accidentally' drink. I'm generally more concerned with dehydration when doing physical stuff like skiing or coping with the heat. Contrary to popular belief a cup of coffee does not contain enough caffeine (which is a diuretic in higher doses in some people) to cause issues so a coffee break is good. But alcohol does so beer is not going to help.