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 is great advice and took me far to long to learn; I also tend to spare a little pasta water to pour over the pasta at the end, and remember to stir a ton!
For first timers, start w penne. Also, caveat: if using a gf replacement like banza, the noodles both seem to absorb less water, and expel more starch into the water. so the mod is to put about an inch of water extra than what you would normally use for flour pasta.