Legionella water monitoring
Know What Your Water Did All Week
GDS installs sensors on your hot and cold water lines, feeds the readings into your building management system, and alerts your team when temperature or flow drifts outside the limits in your water management plan.
Why continuous monitoring
The Gap Between Samples
A quarterly sample tells you about one tap on one morning. It says little about the weeks in between. Continuous monitoring records the conditions that let Legionella grow, around the clock, at the points your plan identifies, so your team can act on a drift early instead of finding it at the next sample.
Legionella bacteria, the cause of Legionnaires' disease (a potentially fatal respiratory infection), thrive in the complex water systems of hospitals, senior living facilities, hotels and cruise ships. The bacteria occur naturally at low levels. Aging infrastructure, stagnant branches and thermal drift turn a background presence into an outbreak, and immunocompromised people are affected first.
Engineering mission-critical monitoring and control systems since 1975.
Why it matters now
Why Facility Teams Are Being Asked for More
CDC reports that U.S. Legionnaires' disease cases have grown nearly ninefold since 2000. The drivers are structural: an older and more immunocompromised population, aging building water infrastructure and warmer water temperatures. Regulators, surveyors and insurers have responded by asking for evidence, not intent. Here is what has moved recently.
Summer 2026NYC Health Department
Upper East Side cluster reaches 94 cases and 11 deaths; 83 buildings ordered to disinfect cooling towersThe cluster was found through case reporting, not building data. Buildings with continuous operating records could show investigators where their own systems stood; the rest had to reconstruct it.
August 2026Office of the Governor
New York State requires twice-yearly cooling tower certification in New York City and raises finesOwners now have to vouch for the condition of their systems on a schedule, which puts a premium on records that show how those systems actually ran.
Effective May 2026NYC Health Department
NYC Local Law 159 moves cooling tower Legionella testing from every three months to monthlyTowers in use must now be sampled at least every 31 days and receive a summer biocide treatment. Sampling frequency is climbing, and the documentation behind it climbs too.
2025 vs. 2024NC Department of Health and Human Services
North Carolina reports 310 Legionnaires’ disease cases in 2025, up from 201 in 2024A 54% increase in one year, in a state far from the usual outbreak headlines.
2025 outbreak, 2026 lawsuitsNYC Health Department; ABC7 New York
Central Harlem outbreak ends with 118 cases and 7 deaths; lawsuits allege cooling tower failuresThe suits name the city, its hospital system and contractors, not only the building owner. When questions come later, a record of what was monitored and when is what a facility can point to.
VA OIG 22-03247-198VA Office of Inspector General
VA OIG audit found incomplete prevention plans, inconsistent sampling, remediation gaps and inconsistent reporting at VA medical centersThe findings centered on documentation and follow-through rather than plan design. Automated logging takes the record-keeping part of that problem off manual rounds.
External links go to the health department, regulator or original reporting. Figures reviewed September 2026.
Instrumentation and alerts
What the System Watches
- Continuous monitoring, permanently in place. Stationary sensors installed in the plumbing record readings automatically and feed your Building Management System. That is the continuous, automated temperature monitoring VHA Directive 1061 calls for in VA drinking-water systems.
- Hot and cold water oversight. Dual-temperature tracking across supply lines and returns, because cold lines running warm are as much of a problem as hot lines running cool.
- Flow and stagnation. Low-use branches, seasonal wings and rooms out of service are where water sits long enough to matter. Flow data at the points you instrument surfaces them without a walkthrough.
- Deviation alerting. When a reading leaves its control limit, the people responsible are notified right away, so staff can act before a drift becomes a pattern.
- BMS integration and reporting. Automated reports, trend analysis and audit trails, so compliance documentation is a byproduct of operating the system rather than a separate project.
Standards and surveys
Where the Data Lands in Your Program
Every one of these frameworks asks the same underlying question: can you show that your control measures held? Monitoring is what turns a written plan into an answer.
VHA Directive 1061
VA buildings with overnight stays
What it asks for
Continuous, automated monitoring of hot and cold water temperatures at the incoming supply, storage tanks, heater discharge, loop returns and representative outlets, with readings reviewed at least weekly.
What our system contributes
Automated sensors at those points, connected to your building automation system, with the retained history and weekly review reports behind each one.
CMS water management expectations
Hospitals, critical access hospitals, nursing homes
What it asks for
A water management program with control measures, control limits, monitoring procedures and corrective actions that surveyors can review.
What our system contributes
Continuous readings at the control points your plan defines, plus timestamped deviation alarms that show the program was actually run.
ASHRAE 188-2021
Most building water systems; referenced by CMS and by state and city codes
What it asks for
For each control point: a control limit, a monitoring procedure and a corrective action when the limit is exceeded.
What our system contributes
Instrumentation at the control points identified in your hazard analysis, with the trend history behind each one.
ASHRAE 514-2023
Buildings adopting the broader water risk standard
What it asks for
Risk management across physical, chemical and microbial hazards, not Legionella alone.
What our system contributes
The same sensor and data layer extended to the additional parameters your program specifies.
Joint Commission PE.04.01.05 / EC.02.05.02
Accredited hospitals (PE.04.01.05) and nursing care centers (EC.02.05.02)
What it asks for
A water management program that addresses Legionella and other waterborne pathogens, and evidence during survey that it is being followed.
What our system contributes
Reports and audit trails generated from logged data rather than transcribed from manual rounds.
NYC cooling tower rules (Local Laws 77 and 159)
Registered cooling towers in New York City
What it asks for
Registration, a maintenance program, monthly Legionella testing by a certified lab while towers are in use, and auditable records.
What our system contributes
Listed for context. We do not perform lab testing, and our monitoring covers building hot and cold water lines, not cooling towers.
Requirements vary by jurisdiction and accrediting body, and editions change. We build to the program your water safety team has already written.
Scope
Where GDS Fits
Water safety involves several vendors, and unclear boundaries are how gaps form. Ours are simple.
What We Engineer
- Sensor selection and placement against the control points in your plan
- Stationary sensor grids, and mobile units where permanent installation does not fit
- Integration into your BMS and existing SCADA infrastructure
- Alarm thresholds, notification paths and escalation logic
- Data retention, trend analysis and audit-ready reporting
- Commissioning, operator training and long-term support
What Stays with Your Other Partners
- Laboratory analysis. Culture and PCR testing stays with your certified lab. Many jurisdictions require a state-approved one.
- Chemical treatment. Disinfectant programs and remediation stay with your water treatment provider.
- The written program. Your water management team owns the hazard analysis and the control limits. We instrument what they decide.
Saying this plainly matters. When a monitoring vendor implies it covers testing and treatment, facilities can end up believing a gap is closed when it is not.
Applications
Facilities We Design For
VA and Healthcare Facilities
Designed around VHA Directive 1061's continuous monitoring requirement and CMS water management expectations, for the population least able to absorb an exposure.
Senior Living
Long corridors, variable occupancy and rooms that sit empty between residents. Stagnation risk is structural here.
Hotels and Hospitality
Seasonal wings and low-occupancy floors create the same conditions, with guest-facing exposure and reputational stakes.
Cruise Ships
Dense potable systems in a confined environment, operating under their own inspection regime.
Delivery
How a Deployment Runs
- 1Walk the systemWe map the water system with your water safety team and identify where monitoring would actually change a decision.
- 2Specify against your control limitsSensor type, placement and interval are driven by the limits already written into your program, not a standard package.
- 3Integrate and configurePoints land in your BMS or SCADA environment. Alarm thresholds and escalation paths are set with the people who will answer them.
- 4Commission and validateWe verify readings against reference measurements and confirm the reports contain what your team and your surveyors need to see.
- 5Support and expandThe architecture supports IoT upgrades, cloud analytics and additional buildings as budget cycles allow.
Why GDS
Controls Engineers, Not Resellers
- Healthcare focus. Our monitoring systems are designed around the continuous monitoring VHA Directive 1061 requires in VA hospitals, where infection control has the least margin for error.
- Five decades of controls work. GDS has engineered mission-critical monitoring and control systems since 1975, across defense, aviation, water and municipal infrastructure. A water monitoring system is a controls project, and it fails in controls-project ways.
- Custom engineering. From stationary sensor grids to mobile units, each system is engineered to your facility's layout, risk profile and compliance obligations.
- Future-ready architecture. Scalable to IoT upgrades, cloud analytics and smart-building integration, so today's installation is not next decade's rip-out.
Common Questions
- What does the system actually measure?
- The conditions that let Legionella amplify: water temperature on both hot and cold lines, flow and stagnation. Those are the parameters a water management program sets control limits against, and they are the ones that drift quietly between manual rounds.
- Does this replace Legionella culture or PCR testing?
- No. Lab testing tells you whether the organism is present at a point in time. Continuous monitoring tells you whether the conditions that allow it to grow were present between those samples. Programs need both, and our systems are built to sit alongside your certified lab and water treatment vendor rather than replace either.
- How often is data collected?
- Around the clock. Our standard configuration logs every sensor every 30 minutes, and the interval is configurable where your program calls for something different. Alarms are evaluated as readings arrive. For VA facilities, VHA Directive 1061 requires continuous, automated temperature monitoring with readings reviewed at least weekly, and the logged history supports that review.
- Will it integrate with the BMS we already have?
- Yes. Sensor data syncs into your Building Management System so water safety parameters live on the same screens as the rest of the building, rather than in a separate portal. We confirm the interface and point capacity during design.
- What if a building has no BMS to integrate with?
- The architecture scales down as well as up. We build to the facility you have, and the same system can grow into IoT expansion and cloud analytics when the building modernizes later.
- What about areas where permanent sensors are not practical?
- We engineer mobile units for locations where a permanently integrated sensor grid does not fit the layout or the renovation schedule.
- What do we hand a surveyor or an investigator?
- Automated reports, trend analysis and audit trails drawn from the logged record. If questions are ever asked about your building, you have the history itself instead of a reconstruction project.
See also our water and wastewater SCADA and HMI modernization work.
Related Insights
Healthcare SCADA
Hospital Water Monitoring: SCADA & Automation →
How SCADA records water temperatures and operating conditions to support a hospital water management program.
Water and Wastewater
SCADA Historian and Reporting for Water Operations →
How to structure historians, trends, and reports so SCADA data supports compliance, troubleshooting, and operational decision-making.
HMI and Software
SCADA Alarm Rationalization and Priorities →
How to rationalize SCADA alarms so operators get fewer nuisance alarms and faster response to real events.
Request a Monitoring Review
Send us your water management plan's control points, or just describe the building. We will come back with where continuous monitoring would close a real gap and where it would not, along with a rough scope.
If you are responding to an RFP, a survey finding or a positive result, say so in the message and include the deadline.