How can I tell if my tomatoes are being underwatered and what steps can I take to ensure they receive the proper amount of water?

You can tell if your tomatoes are being underwatered if the leaves start to wilt and the fruits are small and shriveled. To ensure they receive the proper amount of water, water them deeply and consistently, making sure the soil is moist but not waterlogged. Consider using a drip irrigation system or watering in the morning to prevent evaporation.