Here's How Much Water You Should Put In Your Pasta Pot, According To Alton Brown - Tasting Table

"If you've learned to hold on to your pasta water after boiling, there is a good chance you have Alton Brown to thank for that bit of wisdom. Through his many years as an author and the host of Food Network's "Good Eats," Brown helped pioneer a science-based approach to cooking that has enriched home cooks everywhere. Its led to unusual but amazing suggestions like adding mayo and water to scrambled eggs before cooking."

"One of Brown's best tips for cooking pasta is that you only need to fill your pot enough to cover the pasta. In fact you can pour your pasta in first, then add the water until the pasta is submerged - because another tip from Brown is starting your pasta in cold water. Not only does this save water, but it means the water will boil faster."

Keep pasta water after boiling because its starch enhances sauces. Only fill the pot enough to barely cover the pasta; pouring pasta in first then adding water and starting in cold water saves water and brings the pot to a boil faster. Less water yields a higher concentration of starch in the leftover cooking water. Starchy pasta water helps thicken sauces gently and acts like a gentle thickening agent. Starch also helps sauces emulsify and prevents them from breaking. High-starch pasta water is particularly useful for emulsified dishes such as carbonara.

Read at Tasting Table