The best hypothesis for this scenario is:
"Bean plants will grow best when receiving a moderate amount of water, and excessive or insufficient water will result in stunted growth or plant mortality."
This hypothesis acknowledges that while water is essential for plant growth, there is likely an optimal range of water that supports healthy growth. It suggests that both too much and too little water could negatively impact plant development, which aligns with common understanding in plant biology about the importance of balance in water supply.