Pasta – Should I salt water for cooking pastas based on the volume of water or amount of food

The salt adds flavor, but it also helps reduce the gelation of the starch in the pasta. The starch in food is the form of microscopic grains. When these grains come into contact with water, they will trap some of it (think cornstarch in cold water), but when the water is hot they swell up like balloons and merge with each other, and you have starch gelation.

Another thing you may want to add to the pasta water is some acid (lemon or cream of tartar). Tap water in most cities is made alkaline, which increases the starch loss from the pasta to the water, making the pasta stickier.

For rice it depends.  Cooking any starch in water will first cause the starch granules to swell and eventually tangle up with each other (the gelatinization).  Dissolving sugars or salts in the water slows down the process by raising the temperature the swelling starts.  While few prefer pasta as a stuck blob of strands, the same is not the case for rice.  I like my Basmati loose, but my risotto and sushi sticky, so salt may be required for Basmati and optional for Arborio.

There are many techniques for controlling the starch for rice.  To control the starch gelatinization of rice:

1. cook it like pasta with lots of water, then drain; or 
2. par cook it

Method 1 won't avoid the grain surface starch gelatinization, but it will help with stickiness (you may oil coat it after draining).  Method 2 delays the starch release allowing you to finish a risotto in seven minutes. Cool for parties or for restaurants.