Over-watering a bean plant will kill it. When in the seed stage, too much water can ruin the germination process and when the plant is growing, over-watering can cause disease. If the bean leaves begin to develop small, discolored spots, you may have leaf blight, a common disease of over-watered plants.
It is important not to add onions or fennel to the area around which you are growing your beans. They will inhibit the growth of the bean plant, as the two plants compete with one another for soil and nutrients.
Small amounts of salt in the water is OK--but if the water you use to hydrate the bean plants has too much salt in it, it will kill the plant. Plant cells do not like salt.