In recent years it has become clear that it is actually possible to drink too much water. While the applications are more to exercise lasting longer than four hours in duration, there are possible applications to rowing. Note also the final resource from the American College of Sports Medicine that mentions this condition may be more prevalent in women with smaller body mass.
From USA Track and Field:
"A potentially fatal condition, hyponatremia most often occurs in exercise lasting four hours or longer and results primarily from consuming excessive fluids and is exacerbated by not replacing sodium losses. Severe cases of may involve grand mal seizures, increased intracranial pressure, pulmonary edema (fluid in the lungs), respiratory arrest and even death."
Wikipedia notes that, "Consuming as little as 1.8 liters of water in a single sitting may prove fatal for a person adhering to a low-sodium diet, or 3 liters for a person on a normal diet." And refer to a famous case of fraternity hazing where a student, forced to consume excessive amounts of water died of heart failure.
How many coaches have asked their coxies to drink huge volumes of water to "make weight"?
This is worth at least keeping in mind for rowers even if it typically only occurs in exercise lasting longer than four hours.
It is one on the reasons researchers are now suggesting that athletes consume sports drinks rather than just water as sports drinks contain electrolyte and diminish the possibility of diluting ones plasma electrolytes.
Even if rowers will not reach this point in a 2+ hour workout one wonders if drinking too much before exercise (AS some athletes actually do) and then continuing strong hydration during training on only water could at least put athletes in a position of diminished performance.
For an even more detailed explanation see the American College of Sports Medicine: who have released this very important paper