if you're using water straight from the tap, that may be why.
cold water isn't good for the plants and the chlorine isn't either. if you treat with a water softener, then that is really bad for the plants.
if have a softener system, you'll need to draw water for the plants at a point before the system. if you don't have a softener, just let the water sit overnight in gallon water jugs...the chlorine will have dissipated and it'll be at room temp - perfect conditions.
if your water has fluride added, you'll need to buy water that doesn't have any of that in it...it's bad for the plants.
you could also not be watering thoroughly enough. what types of plants do you have and what kind of soil are they in and what kind of pots (plastic, unglazed, glazed, with/without drainage)??