Why these decisions matter now
Published regulation 28(4) notices can require online monitoring with alarms and fail-safe shutdown. The Drinking Water Inspectorate’s Drinking Water Safety Plan guidance states that monitoring linked to an automated corrective action could be considered a control measure. Where the system that acts on a reading is remote from the instrument, the action also depends on the connection that carries the reading.
Monitoring points that report over an analogue line need a new path before 31 January 2027. Those that rely on 2G-only devices will need an alternative connection before the service closes, which may require a site visit. That replacement work provides a natural opportunity to decide which networks each device can use and which monitored assets need connectivity through independent operator cores.
A late reading that delays corrective action may lengthen an event. The Inspectorate’s Event Risk Index multiplies the maximum population affected by the duration in hours. At the same population, twelve hours instead of six doubles the impact score.
For river monitoring, Defra’s provisional technical guidance sets out measurement at least every hour, and at least every 15 minutes while a storm overflow operates. Defra’s government response states that water companies will be required to complete rollout at 25 per cent of all sites by 2030.
The position as at 4 November 2026
Both guides cite their sources and state the published position on that date, including:
87 notices: issued by the Drinking Water Inspectorate in England in 2025 under regulation 28(4), more than any other kind of legal instrument it used
31 January 2027: the date by which Openreach states that all traditional phone lines will be going digital
2029 to 2030: the UK 2G switch-off dates the mobile operators have announced, as Ofcom lists them
One hour: the period within which Defra’s provisional technical guidance states that water quality data must be made publicly available
15 minutes: measurement at least this often while a storm overflow operates or final effluent quality is, or could be, affected
25 per cent: the share of all programme sites that Defra’s government response states water companies will be required to complete by 2030
10 per cent: the limit on sensor-fault downtime in section 4.3 of the assurance standard, which does not mention the rest of the path
98 per cent: Ofwat’s 2029/30 uptime target for event duration monitors, a separate programme, which leaves about 175 hours a year without a reading
Each guide also sets out what its evidence does not establish.
Recommended for
- Water company board members and executive teams
- Directors responsible for drinking water quality and regulatory compliance
- Leads for continuous water quality monitoring programmes
- Telemetry and control system engineering managers
- Programme leads replacing analogue lines and 2G devices
- Procurement and contract managers for monitoring services
A reading depends on the path it takes
An instrument can measure correctly and still leave a gap in the record. Each reading has to reach the system that records it, raises an alarm or publishes it.
On a mobile network, that path runs through the core of the operator that issued the SIM. A fault in that core can interrupt every device that depends on it, whichever radio network each has joined.
A multi-network SIM lets a device use several operators’ radio networks, but the issuing operator’s core still authenticates it. A second profile on an independent core removes that shared point of failure, provided the equipment switches to it by itself.
For river monitoring, the reporting path has five parts, and different organisations can supply them. Each supplier can meet its own specification while a reading still reaches the public after the hour.
Which monitoring points depend on a single operator core, and what evidence will show that readings reach the public within the hour?
CSL provides the communications link as a managed IoT connectivity service. CSL DualCore® gives each site two secure, independent mobile-core paths, delivered through rSIM® technology or a CSL DualSIM® Router configured for core independence. With rSIM technology, the SIM tests the active path and can switch profile if the test fails.
Download the board guides
Complete the form to download both guides:
Continuous Monitoring in Drinking Water Supply: How to match monitored assets with the appropriate level of connectivity resilience
Continuous Water Quality Monitoring of Rivers: How to define publication within the hour and demonstrate that the outcome has been achieved
To discuss connectivity for a monitoring estate or programme, email sales@csl-group.com.
