By Harold McGee
It’s generally recommended that pasta be cooked in 10 or more times its weight of vigorously boiling water (around 5 quarts or liters water per pound/500 gm). This allows for the pasta’s absorption of 1.6–1.8 times its weight, and leaves plenty to dilute the starch that escapes during cooking, and to separate the noodles from each other so that they cook evenly and without sticking. Hard water—water that is alkaline and contains calcium and magnesium ions—increases both cooking losses and stickiness in noodles (it probably weakens the protein-starch film at the noodle surface, and the ions act as a glue to bond noodle surfaces to each other). Most city tap water has been made alkaline to reduce pipe corrosion, so pasta cooking water can often be improved by adding some form of acid (lemon juice, cream of tartar, citric acid) to adjust the pH to a slightly acidic 6.