Adding cold water during cooking of beans and cooking time After soaking dry beans, I place beans on heat, so they boil for couple of hours, and they cook pretty well. But if I add just one cup of cold water (at room temperature) during boiling, temperature of the mixture would drops for some minutes. But then the cooking time of the beans would increase significantly, and it seems they wouldn't cook well ever.

For most of the beans I experienced this process, but I can't figure out why?
If you want to speed up the cooking time and need to add more water, heat it on stovetop or in microwave till steaming, then add.  Cook at lower heat just at or below simmer to keep beans more intact and with a cover on to avoid water loss in the first place. NEVER add salt at the beginning of the cooking process, only once desired doneness has been reached.  If they just won't get soft (really hard water), add a tablespoon of baking soda to the cooking water, but then they will get soft really fast so watch carefully.