E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Dont rile the water. Do not stir up the water and make it muddy. The water is riledmuddy and unfit to drink. Common Norfolk expressions; also, a boy is riled (out of temper). Isy, together, Joe Smith was regularly riled, is quite Norfolk. The American roil has the same meaning. A corruption of [em]broil. (French, brouiller; our broil.) The adjective rily, turbid, angry, is more common.