One idea, you could combine them something similar like how broadband devices, say like the laptop, picks up other networks if your device is in range of them. The laptop could detect any number of networks on the one reciever.
Maybe if the handheld device was the same type of thing and picked up signals from both the power meter and the water meter to the one reciever and then had both the readings displayed on the small digital screen of the reciever.