I'd soak in cold water- not warm or hot. Maybe only 10 minutes on thin skinned produce.
Actually- what I've been using is Veggie Wash - a 100% organic produce cleanser made from citrus . You spray it on the veggie or fruit and rub for 30 seconds, then rinsed with cold water. I get it for $3.69 at our local Wegman's store.
The instructions for lettuce is to soak in cold water with a little of the "veggie wash" in the water for a few minutes- then rinse and spin dry.