Not enough info, so all I can say is when they need it - are we talking in pots, or in the ground, in sun or shade, and how old are the plants?

You need to keep them well watered regardless of if its a hot summer or not as they are forming the new flower buds for next year, failure to do this will result in poor flowering and some of the buds going brown and falling off, aprox seven years ago i did a planting scheme of rhodis and azaleas for this lady, and throughout the summer we have kept them well watered, twice a week, also in early may i sprinkle round the base of each plant plenty of rotting pine needles and gently hoe them in, they love it, the foliage is always a healthy deep green no signs of yellowing, i also water them through the winter if we get a dry spell. julien