Yes, overwatering a lilac bush can indeed be detrimental to its health. Lilacs are hardy plants that are relatively drought-tolerant and prefer well-drained soil. Overwatering can lead to a condition known as "waterlogging" which can suffocate the roots, inhibiting their ability to absorb necessary nutrients from the soil. This can cause the leaves to yellow and wilt, and in severe cases, it can even lead to the death of the plant. It's crucial to ensure that lilacs are watered appropriately, which generally means watering deeply but infrequently. The soil should be allowed to dry out between waterings to prevent over-saturation. Always remember, the key to a healthy lilac bush is balance when it comes to watering.