They say that the water you boil your pasta in has most of the vitamins and nutrients in the pasta and by throwing it out, you are wasting it. I do not know if this is true but wasting water does not make sense to me anyway.
I usually cook my pasta in very little water and by mixing the pasta frequently, I let the it absorb all the water and if it is not cooked yet, I just add some more water. This way there is no water to dump when you are done. However, sometimes it is not easy like when you are using large pasta such as penne. I then use more water but take the pasta out and use the remaining water to make a soup. This is an especially good strategy when I am making meat filled dumplings (manti).
I have a water saving strategy for the shower as well. The hot water is centrally heated at my apartment. They have these meters that they track our usage and the Apartment Management bills us depending on the usage. I have realized that I let at least half a bucket of water run before I can comfortably step under the shower. So, I keep a bucket by the bathtub and save that half a bucket of water to later dump in the toilet. It is so easy. I am probably saving very little money but knowing that a large portion of the human population has very limited access to water, these tactics make me feel like I have done something that has value.