The Elster A1700 is a 3 phase electricity meter.
You can buy a slot-in module that counts pulses and then setup the A1700 to profile those pulses.
You can then connect the pulse counter to your water meter and setup PnPScada to read that profile.
Info on the pulse counter module can be found here on Elster's website.

You first need to program the Elster A1700 to profile the pulse counters.
In PMU create a new scheme by going to File->New->A1700 Scheme
In scheme editor, tick the Load profile definition checkbox
Select Compatability
Untick everything except Multi Utility A1700 (Vision) P********-4 and select OK
Tick Import W and Q1 Inductive Import and Input 1
You can now send this scheme to the meter by clicking on the red arrow.

To configure this on PnPScada, add the Elster meter as you would normally add it as a power meter.
Then add the water meter as a pulse meter.
When asked "This entity needs 1 or more Pulse Counters to function", in the dropdown, choose the A1700 with External 1.