What technology there is to transmit data from digital water flow meter?

Most industry use a 4 to 20 milliamp loop on a 24 volt DC supply line. One can put the 4 to 20 ma signal into an input module on a PLC and configure the PLC for monitoring it. If your input module only monitors voltage, then one put a 250 ohm resister across the input terminals of the input module and it converts to 1 to 5 volts DC.