We are having a drought in California, so I'm just wondering if I could reuse salted pasta water (after it cools) to keep the plants hydrated. Is this a good idea?
If you're having a drought, I'd say you'll be fine using it for a short period of time. You mentioned adding salt; this will build up in containers every day you use it, and eventually will harm the plant. Don't use for prolonged periods, and dilute it if possible, as far as possible.
Pasta water contains residue full of carbohydrates, so the bacterial activity in the soil will benefit, but it may cause a layer on top of the soil. Also, be sure the water was well strained, because it's not best to leave pieces of pasta in the plants' pots. The fact that the plants are edibles shouldn't be a problem. The pasta water is non-toxic to humans, so safe to use on edibles.
I wouldn't recommend it long term but in the short term, it should be fine EXCEPT it's salted. Cook your pasta without salt while there's a drought and then use the water. It doesn't really need salt to cook anyway, usually any kind of sauce you're using on the pasta is salted, so its not essential. If you notice a difference in the pasta, return to using salt when the drought is over. Best used on open ground rather than pots, but won't do any harm in pots in the short term (minus the salt). I'm intrigued that you use salt at all when you cook pasta, frankly, I never do.
If you're like me, and use some vegetable oil in the water to keep the noodles from sticking together, you'll want to be careful not to get it on the plant itself. The oil will heat up in the sun and burn the plant.
As for the soil, as long as there is good drainage, I think you should be fine. I might consider not doing so if it's in a container. I'm not sure what effects the oil might have if it sits around the roots, but I would imagine it would suffocate them if it was allowed to collect.
oil and salt in it might indeed be an issue if you are using just this water and in a container or a place where the drainage is poor. I would not do it personally.
Also, the gain is low considering that you will need to make a pot dirty to gather the water and let it cool down, the water you saved is lost when washing that pot...