Replacing a Legacy Water SCADA System: 6 Steps From Assessment to Go-Live

Why Utilities Replace SCADA Systems

Legacy SCADA platforms accumulate risk over time in ways that are not always visible until a crisis forces action. Wonderware InTouch reached end-of-life for versions prior to 2017 in 2022; Schneider Electric's iFIX 5.x series has limited vendor support; Citect SCADA versions prior to 2016 receive no security patches. An unpatched SCADA system running Windows XP or Windows 7 — the operating systems many legacy systems require — has hundreds of known exploits available in public databases. The 2021 Oldsmar, Florida water treatment plant incident, where a remote attacker attempted to increase sodium hydroxide (lye) concentration to 111 times the safe level, was enabled by remote access software on an unpatched Windows 7 machine connected to the SCADA system.

Beyond cybersecurity, legacy systems create operational problems: spare hardware for discontinued PLC models (early Allen-Bradley SLC 500, Square D SY/MAX, older GE Series 90) may be unavailable or sourced only from eBay. Legacy SCADA servers running proprietary database formats cannot exchange data with modern AMI systems, work order management platforms, or regulatory reporting tools. Historian data quality degrades as database files grow beyond the capacity of the original design.

Step 1: Current State Assessment

A thorough current-state assessment is the foundation of a successful replacement project. Rushing to platform selection without understanding the existing system in detail leads to missed requirements, scope creep, and cost overruns during implementation. The assessment should document:

• Hardware inventory: Every PLC, RTU, HMI panel, SCADA server, network switch, and communication device — including model number, firmware version, age, and physical condition.
• Software inventory: SCADA application version, operating system version, installed patches, license status, third-party drivers and OPC servers, historian type and configuration.
• Network diagram: OT network topology, IP addressing scheme, communication paths between field devices and SCADA servers, remote access methods, firewall and security appliance configuration.
• I/O count and tag database: Total number of analog inputs, analog outputs, digital inputs, and digital outputs per site. Tag naming conventions. Critical tags that require continuous monitoring vs. low-priority status tags.
• Integration points: All external systems that exchange data with the SCADA — billing systems, AMI platforms, laboratory information management systems (LIMS), regulatory reporting tools, customer portals.
• Operator interviews: Structured interviews with operators and control room staff to document pain points, workarounds, missing functionality, and features they value in the current system. Operators who use the system daily often have detailed knowledge of undocumented behaviors and integration points that are not in any engineering drawing.

Step 2: Requirements Definition

Requirements definition translates the assessment findings and operator input into a documented specification that drives platform selection and project scope. Key requirements categories for water utility SCADA replacement:

• Reliability targets: Required system availability percentage (99.5%, 99.9%?), maximum allowable downtime per year, redundancy requirements for SCADA servers, historian, and network infrastructure.
• Reporting requirements: Regulatory reports required by TCEQ or EPA, frequency and format of each report, whether the SCADA system must generate the reports directly or only provide data export to reporting tools.
• Number and type of sites: How many remote sites require SCADA connectivity? What communication infrastructure exists at each site? Which sites require local HMI panels vs. remote-only monitoring?
• Cybersecurity requirements: Does the utility follow AWWA Cybersecurity Guidance, NIST SP 800-82 (Guide to ICS Security), or ICS-CERT recommendations? What authentication, audit logging, and network segmentation standards must be met?
• Operator interface preferences: Alarm display requirements, trend display requirements, geographic system overview display, mobile access requirements.

Step 3: Platform Selection

Three SCADA platforms dominate municipal water utility projects in 2025–2026:

• Inductive Automation Ignition: Browser-based architecture with unlimited client licensing (a single server license supports unlimited HMI clients and historian connections). Ignition's Perspective module provides responsive web-based HMI accessible from any browser, including mobile devices. The platform uses a tag-based historian (MySQL or SQL Server backend) with standard SQL access. Ignition is the fastest-growing platform in water/wastewater and is particularly strong for utilities that want IT/OT integration and custom reporting. Pricing is per server, not per tag — significant cost advantage for large tag-count systems.
• Rockwell Automation FactoryTalk View SE: The incumbent platform for utilities with significant Allen-Bradley PLC infrastructure. Deep integration with Studio 5000 PLC programming environment, ControlLogix and CompactLogix PLCs, and the FactoryTalk Historian (based on OSIsoft PI). FactoryTalk licensing is per-client-seat and per-tag, making large-scale deployments more expensive than Ignition. Strong installed base in Texas water utilities with experienced local integrators.
• AVEVA System Platform (formerly Wonderware): Enterprise-scale SCADA platform with strong process industry heritage. ArchestrA object-based architecture enables reusable templates for pump stations, well sites, and treatment trains, reducing configuration time for large multi-site utilities. AVEVA is best suited for utilities with 50+ remote sites where template-based configuration provides efficiency gains. Higher licensing cost and implementation complexity than Ignition for small to medium utilities.

Platform selection criteria should include the availability of qualified local integrators (a platform requiring consultants to fly in from another state increases cost and support response time), compatibility with existing PLC hardware where PLCs are being retained, and the utility's internal IT team's familiarity with the server operating system and database platform.

Step 4: Migration Strategy

The migration strategy defines how the utility transitions from the old system to the new system without interrupting water service or creating monitoring gaps. Three migration approaches are used in practice:

• Parallel operation: The new SCADA system is commissioned alongside the existing system, both connected to the same field devices simultaneously. Operators monitor both systems for a defined period (typically 30–90 days), cross-checking readings and alarm behavior. Cutover to the new system as primary occurs only after both systems agree and operators are confident. This is the safest approach but requires the most hardware and temporary infrastructure investment. Parallel operation is mandatory for critical treatment facilities where monitoring gaps are unacceptable.
• Cutover approach: The old system is decommissioned site-by-site as the new system is commissioned. Appropriate for smaller systems or individual remote sites where a brief monitoring gap is acceptable and the old system's reliability is poor enough that parallel operation provides no safety benefit.
• Site-by-site rollout: For multi-site utilities with 20+ remote locations, the new SCADA platform is deployed at the central server first, then remote sites are migrated one at a time over 12–24 months. Early sites serve as learning experiences that improve configuration efficiency for subsequent sites. This approach manages project risk by distributing implementation across time while maintaining the existing system for un-migrated sites.

Step 5: Panel and Field Work

Panel and field work is typically the longest phase of a SCADA replacement and the most disruptive to operations. Tasks include:

• PLC replacement and I/O rewiring at remote sites (often requiring brief site shutdowns coordinated with operations staff)
• Fiber optic or cellular network infrastructure upgrades to support new SCADA communication requirements
• New HMI panel installation at remote sites requiring local operator interface
• SCADA server hardware installation in the control room, including UPS, network switches, and firewall appliances
• Cable labeling and documentation update concurrent with rewiring

Step 6: Commissioning and Training

Commissioning verifies that the installed system meets the documented requirements before operators rely on it for production use. A structured commissioning process includes: Factory Acceptance Test (FAT) at the integrator's facility using a simulated I/O environment, Site Acceptance Test (SAT) at each remote site verifying all field connections and communications, and integrated system testing at the control room verifying historian, alarm, and reporting functions. Operator training should be hands-on, conducted at the utility's actual SCADA workstations, and tailored to the operators' existing SCADA knowledge rather than generic vendor training. A 90-day warranty support period following go-live, with the integrator available for rapid response to issues, is essential for building operator confidence in the new system.

Typical timeline for a medium water utility (15–30 remote sites): 12–18 months from assessment to full go-live. Larger utilities with 50+ sites and complex treatment plant controls may require 24–36 months.

NFM Consulting Water Automation Services

NFM Consulting manages water SCADA replacement projects from initial assessment through go-live and beyond. We specialize in Ignition and Allen-Bradley FactoryTalk implementations for Texas water utilities, providing full-scope services including hardware procurement, panel fabrication, field installation, software configuration, historian setup, operator training, and ongoing support. Contact NFM Consulting to schedule a legacy SCADA assessment for your utility.