You want to save water when boiling pasta? Stop using a big pot.

Pour the pasta into a skilled, add enough water to completely cover it and turn on the heat. Add a pinch of salt (not too much, as you will be eating all of it) and allow the pasta to cook. It will slowly absorb the water it needs and will normally leave little to none behind. If some water is left behind, use it to thicken sauces; the gluten in the water helps.

This works with every pasta, even spaghetti.