Combine water, 2 tablespoons sugar, and cornstarch in a small saucepan. Cook over low heat, stirring constantly, until clear and thickened, about 2 minutes. Remove from heat.

Beat egg whites, cream of tartar, and salt in a large glass or metal bowl until foamy. Add vanilla. Gradually beat in remaining 6 tablespoons sugar until soft peaks form. Gradually beat in cornstarch mixture until stiff, glossy peaks form. Spread meringue over hot pie filling, sealing to the crust. Brown in the oven as desired.