It is true that the higher the humidity in the enviroment the flatter the print will dry if left alone. But it's really not necessary to leave the water on the print to aide in this. In fact it could cause problems if there is any impurities in your water that could leave a dry deposit on the prints surface. Another method is just the reverse - dry the print as quickly and evenly as possable using a hair dryer. Dry the face first until just dry to the touch, turn the print and repeat on the back, turn and repeat on face and then back to the back. Repeat this process until just dry. Then stick in press or as was mentioned, between matt boards with weight.