Drugs.com states that while there are no known side effects of using sterile water in small doses, one should never take it intravenously. The Patient Safety Authority of the Commonwealth of Pennsylvania asserts that intravenous use can cause serious harm, hemolysis or death.
Sterile water is a hypotonic solution, according to Drugs.com. Therefore, when injected into the bloodstream, it causes water to move into blood cells by osmosis. The blood cells swell with the excess fluid and eventually burst, potentially resulting in death if not treated.
Childbirth Connection lists many advantages to injecting a small amount of sterile water just beneath the skin at locations in the lower back, to reduce labor pain. The only side effect noted with this method is a stinging sensation at the injection site when administered. This injection method can be repeated without further adverse effects.
The Pennsylvania Patient Safety Authority states that in the event of hypernatremia, which is a high level of blood sodium, sterile water can be taken by mouth or nasogastric tube to help correct the electrolyte imbalance. No side effects are listed for ingestion.
Drugs.com recommends seeking medical attention immediately if experiencing severe side effects such as allergic reaction, fever, redness, swelling or tenderness at the injection site.