With too much water consumption at once, the blood will become much more hypotonic. Therefore, a larger amount of water will remain in the blood as the kidneys cannot ultrafiltrate all water out from the blood. Therefore, the blood will be diluted, hence the concentrations of electrolytes decreases.
I searched for the illnesses caused by the over-consumption of water. What I mainly found is only hyponatremia, which is low content of Na+ in blood, and the symptoms caused by hyponatremia. However, I am thinking about why seems only the concentration Na+ decreases, but not other electrolytes e.g. K+, Cl-, which are vital for metabolism and homeostasis?