ZombieCake said:
Boiling up spuds, pasta, etc. takes some time and so uses quite more fuel and water as you generally have to drain.
It's a good point about how much fuel and water is consumed. But potatoes can be cooked without water, and it's not difficult to learn to cook pasta in just enough water, so it's all been absorbed by the end of cooking - pasta may end up a bit claggy, but still edible.