In medium saucepan, bring water to boil. Using a sharp knife, cut a shallow “X” on the bottom of each tomato. Place tomatoes in water, cooking until skin is just starting to come away, 30–60 seconds. Remove tomatoes with slotted spoon and rest in ice bath. Peel skins off tomatoes. Purée tomatoes in food processor; pour purée through strainer lined with cheesecloth into medium bowl. Refrigerate remaining tomato water overnight.