I am so glad that you are asking and concerned. BUT I am also perplexed about why you haven't asked your doctor. If you are concerned about finances, and IF you have a regular pediatrician, and when your child doesn't appear ill but you're concerned, perhaps they wouldn't mind your calling or faxing him to ask that question. In those cases, the nurse might ask the doctor and respond back to you to say if and why you need to come in or not. Don't be shy about telling them your financial condition if that's the case. If you don't have a regular doctor but do have insurance, sometimes they have "Ask a Nurse" services (UHC does). You can call them anytime with medical questions. They are terrific. If people on this site suggest anything other than seeing a doctor, don't listen unless they say they are a nurse or doctor or a parent who had the VERY same condition.
Here is a quote from "About.com":
Drinking too much water can lead to a condition known as water intoxication and to a related problem resulting from the dilution of sodium in the body, hyponatremia. Water intoxication is most commonly seen in infants under six months of age and sometimes in athletes. A baby can get water intoxication as a result of drinking several bottles of water a day or from drinking infant formula that has been diluted too much. What Happens During Water Intoxication?
When too much water enters the body's cells, the tissues swell with the excess fluid. Your cells maintain a specific concentration gradient, so excess water outside the cells (the serum) draws sodium from within the cells out into the serum in an attempt to re-establish the necessary concentration. As more water accumulates, the serum sodium concentration drops -- a condition known as hyponatremia. The other way cells try to regain the electrolyte balance is for water outside the cells to rush into the cells via osmosis. The movement of water across a semipermeable membrane from higher to lower concentration is called osmosis. Although electrolytes are more concentrated inside the cells than outside, the water outside the cells is 'more concentrated' or 'less dilute' since it contains fewer electrolytes. Both electrolytes and water move across the cell membrane in an effort to balance concentration. Theoretically, cells could swell to the point of bursting.
From the cell's point of view, water intoxication produces the same effects as would result from drowning in fresh water. Electrolyte imbalance and tissue swelling can cause an irregular heartbeat, allow fluid to enter the lungs, and may cause fluttering eyelids. Swelling puts pressure on the brain and nerves, which can cause behaviors resembling alcohol intoxication. Swelling of brain tissues can cause seizures, coma and ultimately death unless water intake is restricted and a hypertonic saline (salt) solution is administered. If treatment is given before tissue swelling causes too much cellular damage, then a complete recovery can be expected within a few days.