I like this one. The answer is probably
I am generally white, but I can also be pink.
Regular salt is typically white, but Himalayan Rock Salt is pink.
I am popular.
Lots of people put salt on their food.
You can't live without me, but I can kill you.
I can't remember what the exact biological benefit of salt is, but if you eat too much of it you'll die.
I am usually bigger than you would use me.
Salt blocks can be very large.
Sometimes you add elements to me, sometimes you add me to other things, but usually, you do not use me by myself.
People don't typically eat salt by itself- and I guess if the question is referring to Sodium specifically, it's combined with Chloride to form table salt usually.
I come from water, but not from any water.
Salt can be derived from salt water (with extreme difficulty) but not freshwater.
I am part of you.
Salt is a part of all of us.