Ibn Wahb (may Allah have mercy on him) narrates with this same chain that the Messenger of Allah (peace and blessings be upon him) said: "Whatever is watered by the sky, rivers or springs, or is rain-fed, a tenth is due on it; but whatever is watered by drawing water or from wells and the like, half a tenth is due on it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7486