Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "On crops watered by rivers or clouds, a tenth is due; and on what is watered by a water-wheel (from a well) and the like, half a tenth is due."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7488