About a week after planting the seeds, you should start thinking about watering carrots. Carrots require about an inch of water per week to reach their full potential. If no rain falls in your area, you'll need to water the carrots yourself. A slow, deep soak is the best method. You can use a soaker hose or a drip irrigation system, but these options can be expensive. A mist from a garden hose sprayer will do the job just fine.
Young Carrot Tops
Before watering carrots, dig down about 4 inches into the soil beside the plants. If the soil is moist, you're probably in good shape. If it's dry, it's time to water. It's fine if the foliage gets wet. Just make sure to water slowly enough so that no soil is eroded away. You want to water carrots deeply enough so that the bottom of the root gets plenty of water. Imagine that a growing carrot might be 6 inches under the surface of the soil. If the bottom of the carrot doesn't get enough water, it will likely end up deformed or fail to reach its full size potential.