How to use bitter or hard water for cooking and specially in soaking beans

It rather depends on the temperature of the room. Where I live, in the summer it gets hot and humid, and they shouldn't be out on the counter during the day, or they ferment. In winter (like spring in the northern US, 45-70 farenheit) they can be out for two days with no problem.

My recommendation would be to soak overnight for morning use, or to soak during the day for evening use. It also helps to change the water every few hours, though this isn't critical. If you refrigerate them with the water, you get an extra half-day. Refrigerating drained gets another day or so.

Either way, they should always be shaded, never in direct sunlight.

If they do spoil, you'll know, as they'll have a sour/yeasty smell to them.

NO--I cannot emphasize this enough--you CANNOT use nylon rope (or any other random rope you have laying around, unless you can be guaranteed that it is 100% cotton or hemp)! It will melt all over your food. Cooking twine is generally, if memory serves, pure cotton and thus safe (though perhaps not tasty) to eat.

Tying your beans in bundles would be counterproductive; only the outer beans would cook. Unless you did some sort of weaving thing like a bamboo mat, at which point I would have to question whether the extra work actually saved you any time.

The mistake that most people make when grilling long skinny things is, as you say, to roll them. Or to flip them as though they were bigger objects. The trick is to turn them from their ends, so it's just a matter of grabbing the end--straight on, parallel to the bean--with your tongs, twist your wrist, move on to the next one.