You can't overdose on water-soluble vitamins.
Many people think that there's no such thing as taking too much of a water-soluble vitamin. Unlike fat-soluble vitamins, water-soluble vitamins are not stored in the body. Excessive amounts are flushed out of the body into the urine.
But that doesn't mean that taking large amounts of water-soluble vitamins is always safe. The vitamins still have to make their way through the body and they may do damage along the way.
For example, doses of vitamin C greater than 2000 mg/day can cause diarrhea, nausea, and vomiting. In people with a history of oxalate kidney stones, supplemental vitamin C of 1 gram per day may increase stone risk by up to 40%.