In a medium saucepan, bring 2 inches of water to a simmer.
In a large heatproof mixing bowl, combine reserved egg whites, light corn syrup, cream of tartar, water, and sugar.
Place bowl over simmering water (it should not touch water); with a handheld mixer, beat on high speed until stiff peaks form, about 7 minutes.
Remove bowl from heat; beat 3 to 5 minutes more to cool. Use immediately.