Ensuring access to potable water is fundamental to sustaining human life. The systematic treatment of wastewater is essential for protecting public health and the environment. As a result, the reliable delivery of fresh water and the secure collection and handling of wastewater are core responsibilities for every water authority. 

To meet these needs with the high availability required, utilities incorporate secondary control capabilities into their remote water and wastewater control and telemetry systems. Although these high availability measures are often mandated by regulations such as the EPA’s Safe Drinking Water Act, utilities must still achieve them under tightly constrained operating and capital budgets. By using high availability controllers (redundant) control systems, water and wastewater systems can provide reliable potable water delivery and wastewater collection services with a minimum of risk and expense.

Regulations require water and wastewater authorities to maintain independent local control and operational continuity if the control system, communications network, SCADA, or telemetry fail. This doesn’t always require two separate controllers. However, it does require the primary local control panel to keep the process running should the primary controller become unavailable. 

Traditionally, utilities have achieved this through either a secondary controller running simplified logic or through hardwired fallback controls using mechanical relays and floats. Although both methods can meet regulatory requirements, they introduce significant challenges that increase costs and reduce overall operational efficiency. 

Challenges with traditional secondary controllers 

A secondary controller increases both panel cost and wiring complexity, and pairing dissimilar devices adds substantial maintenance burden. A common configuration includes a remote terminal unit (RTU) paired with a programmable logic controller (PLC). Each are programmed with different tools and running separate applications. Even when the secondary controller runs only simple code, operators must still maintain, test, and deploy two applications—often using additional software tools that carry their own licensing, training, and support costs. 

The alternative—mechanical relays and float switches—reduces the need to maintain a second digital controller. It introduces larger, more complex panels and still requires regular testing and maintenance. Both approaches impose significant operational and capital expenses, which are amplified for remote telemetry assets distributed across wide geographic areas.

Benefits of high availability control architectures

A more efficient alternative is a high availability control architecture built around redundant controllers. These systems maintain continuous operation during equipment faults, network failures, or maintenance activities. Schneider Electric’s high availability controllers provide this capability through two identical, real-time synchronized controllers connected directly to the process. User guidance is provided to deploy the controllers in fault‑tolerant architectures with resilient communications.  

Schneider offers high availability automation solutions including the Modicon M580 PLC, with the available Hot Standby feature, and the SCADAPack 470R RTU. When using the Modicon M580 with Hot Standby or SCADAPack 470R: 

• Two identically configured controllers, primary and standby, operate in parallel 
• The primary controller executes the application while continuously updating the standby controller 
• If the primary controller fails, a switchover occurs within one scan cycle—essentially seamless. The standby controller then becomes the primary controller. Status information is provided to the SCADA and operators indicating that a standby controller is no longer available 
• Both controllers monitor system health and initiate switchover automatically 

This approach helps water and wastewater authorities maintain continuous operation with uninterrupted availability. It also significantly reduces the risk of uncontrolled shutdowns. By using two identically configured controllers, utilities can also reduce both operating and capital expenditures by: 

• Simplifying panel and onsite designs by removing additional controllers, extra sensors, relays, and other devices 
• Streamlining SCADA and control room interfaces by monitoring a single redundant controller pair 
• Eliminating the need to design, test, and maintain a dissimilar secondary control system—including associated materials and training 
• Reducing travel requirements to remote, geographically dispersed assets 

Focusing on higher-value work 

A further benefit is that water authorities can focus their OT staff away from maintaining redundant dissimilar control systems. Instead, they can apply their skill and experience to optimizing operations by improving efficiency and performance or addressing real challenges that directly influence their customers.

By adopting modern high availability automation solutions built on fully redundant controllers, water and wastewater authorities can meet stringent regulatory demands while reducing the operational and financial burdens associated with secondary control systems. 

This approach enhances resilience and ensures continuous, uninterrupted service to the communities they support. The solution also streamlines engineering, maintenance, and lifecycle management across widely dispersed assets. 

High availability control architectures enable water utilities to shift their focus from maintaining disparate technologies to driving operational excellence, empowering their teams to invest time and expertise in improving performance, strengthening reliability, and delivering greater value to their customers.