Water Utility SCADA Migration from Dialup to 4G

A regional water utility operating in the North of England faced a mandatory migration of 28 pumping station SCADA outstations from PSTN dialup connectivity to a modern cellular WAN solution. The migration was driven by the BT PSTN switch-off timeline and the need to maintain continuous Ofwat compliance reporting obligations at all sites.

The Challenge

All 28 sites used legacy RTUs communicating via Modbus RTU over RS485 on the existing dialup connection. The migration needed to maintain the existing SCADA polling architecture without requiring RTU replacement at each site – a constraint driven by the cost of replacing operational equipment at 28 sites simultaneously. Connectivity outages exceeding 4 hours at certain sites would trigger Ofwat reporting obligations.

The Solution

Milesight UR35 routers were specified for each site. The RS485 Modbus gateway in the UR35 firmware allowed the existing RTU RS485 wiring to connect directly to the router, with the router presenting the RTU data as Modbus TCP to the SCADA host. No RTU replacement was required at any site. Multi-network SIM cards were installed with dual SIM configuration to provide primary and backup cellular paths. OpenVPN tunnels to the utility’s control centre replaced the dialup connection with encrypted cellular WAN.

Deployment

Sites were migrated in batches of 4-5 per week over a 7-week programme. Each site migration was completed within a 2-hour planned maintenance window. Pre-configured routers were delivered to site ready for installation – the installation team connected the RS485 cable, power, and Ethernet, confirmed DeviceHub connectivity, and closed the maintenance window. SCADA continuity was maintained at all sites throughout the programme.

The Outcome

All 28 sites successfully migrated ahead of the PSTN switch-off deadline. Average cellular connection uptime across the estate exceeded 99.6% in the 12 months following deployment. Two SIM failover events were recorded in the first 3 months, both resolved automatically without operator intervention. DeviceHub monitoring provided the network operations team with real-time visibility of all 28 sites from a single dashboard for the first time in the estate’s operational history.