The condensate hose on the air conditioner slips off its fitting, and instead of reaching the drain, the water runs down the wall and under the nearest rack. By the time anyone notices, it is pooling around the rack feet or spreading out of sight under a raised floor. Good server room water leak detection therefore starts with location: leak sensors belong where water appears, flows and collects, not wherever there is free wall space.
The short answer: a spot probe goes under a known water source or at the lowest point, a sensing cable follows the path water would take, and the transmitter is mounted above anything that could get wet. The often forgotten second half: an alert at 3 a.m. only helps if it reaches someone who knows where to go. The examples here are three LoRaWAN leak sensors: the Milesight EM300-SLD (spot probe), EM300-ZLD (sensing cable) and Dragino WL03A-LB (expandable cable).
Where does water in a server room come from?
In small and mid-sized server rooms, the air conditioner is the most likely source. Every cooling unit produces condensate that leaves through a drain pan, a pump or a hose. If the pump fails, the hose clogs or a fitting comes loose, the pan overflows, usually drop by drop over hours, so it often goes unnoticed until there is a puddle.
Next comes plumbing through or above the room: heating pipes, chilled water lines, and supply or waste lines from upper floors. Add leaking roofs and windows, and in basements sewer backflow or groundwater. The table sorts typical sources by where water shows up first and where a sensing point makes sense.
| Water source | Where water shows up first | Sensible sensing point |
|---|---|---|
| Air conditioner condensate | Wall base below the indoor unit or base of a floor-standing unit | Spot probe directly below, or cable around the unit base |
| Heating and chilled water pipes | Along the pipe run, at joints and valves | Sensing cable on the floor parallel to the run |
| Pipes from upper floors, roof | Unpredictable from above, then at the low point | Low points and wall bases below ceilings with pipes |
| Backflow, groundwater in basements | Floor drain, wall joints, door threshold | Spot probe at the drain, cable along the affected wall |
The pattern: for sources whose location you know, you sense right at the source. Water from above can land anywhere, so you sense where it collects. To find low points, check the floor with a spirit level and note any slope toward the door, drains and joints. A simple sketch of sources, flow direction and racks is the best groundwork for everything that follows.
How many water sensors does a server room need?
There is no fixed number per square meter. A more useful rule: one sensing point per known water source, one per collection point, and a separate zone wherever an alert should send someone to a different place. One sensor covering both the air conditioner and a heating pipe at the other end of the room saves hardware, but in an emergency someone first has to work out which spot is wet.
Take a server room of about 12 square meters (130 square feet) with one row of five racks, a wall-mounted split air conditioner, a heating pipe along the outside wall and a door to the hallway. That room needs three sensing points: a Milesight EM300-SLD with its spot probe below the air conditioner’s indoor unit, a Milesight EM300-ZLD with its sensing cable parallel to the heating pipe, and another spot probe at the lowest point, often the door threshold when the floor slopes that way.
With cables, length matters. According to Milesight, the standard cable on the EM300-ZLD is 3 meters long, roughly the front of five racks that are 600 millimeters wide. Milesight offers longer cables as custom builds, but the standard cable has only one connector and cannot be extended. The Dragino WL03A-LB is designed to be expanded with additional sensing cables, which suits long pipe runs or a full room perimeter better.
We cover the general differences between a spot probe and a cable leak sensor in a separate article. For planning, one point matters most: every sensing point needs a battery, a name, an alert rule and a place on the maintenance list. More sensors only help when each answers a question no other sensor answers.
Where should leak sensors go under a raised floor?
Water that enters a raised floor void from a cooling unit, a pipe or a cable penetration flows across the structural slab and stays invisible. The tiles look dry while a puddle spreads below. A leak sensor on the tiles detects nothing, so the sensing point always belongs on the slab.
Find the low points of the slab, the areas under cooling units that blow into or stand on the raised floor, and the wall penetrations where pipes enter. A sensing cable should lie flat on the slab without gaps, held down with clips. Milesight advises against gluing the EM300-ZLD cable or fastening it with metal, because both can reduce sensitivity. Keep the connectors out of the area that could flood, otherwise you risk false alarms.
Thresholds matter too: per the manufacturer’s guide, the EM300-ZLD only reports a leak once at least 3 centimeters of cable are wet with water at least 1 millimeter deep. The EM300-SLD probe triggers when water reaches both metal pins at the same time. A cable that sags a few millimeters above the slab therefore stays dry while water collects underneath it.
The transmitter does not belong in the void. The EM300 enclosure is rated IP67, but metal floor tiles weaken the radio signal noticeably. Run only the sensing element down and mount the transmitter above the floor; the EM300-SLD probe hangs on a 1.5-meter lead, usually enough for that route. Mark the tiles above each sensing point so nobody removes an unfamiliar cable during a refit. A well-kept leak detection system includes a floor plan showing every sensing point and its tile.
How do you detect a leak from a server room air conditioner?
With a wall-mounted split indoor unit, overflowing condensate almost always runs down directly below the unit, usually on the side with the condensate connection. Put the sensor there, at the base of the wall or in a secondary drip tray. The unit’s own condensate pan is the wrong place: it holds water during normal operation and would trigger a constant alarm.
A separately mounted condensate pump, say in a cable duct or behind a panel, needs its own sensing point. Milesight lists drip trays, floor drains and tight corners as suitable spots for the small EM300-SLD probe. The pins should face where water would come from and must not touch metal, which can cause false alarms.
For floor-standing precision cooling units, a sensing cable around the base works better than a single probe, because water can escape on any side. Per the manufacturer’s guide, the cable should not lie in the air conditioner’s airflow or in permanently damp spots, where condensation can cause false alarms.
The EM300 series also measures temperature and humidity and can raise threshold alarms, so if a fault shuts the air conditioner down and the room heats up, you get a second warning about the same problem. Keep in mind that the transmitter measures where it is mounted, so a unit near the floor reports different values than one at rack intake height.
Data center leak detection: what changes at scale?
In a data center, three things change: run length, leak location and integration. Chilled water pipes run for dozens of meters under the floor, alongside computer room air handlers and a growing number of liquid-cooled racks.
Leak location is the biggest difference. The cable systems named here are zone sensors: they report that water is somewhere along the cable, but not where. Milesight states this explicitly for the EM300-ZLD, and Dragino describes the WL03A-LB as a non-positioning rope sensor. With 3 meters of cable that is fine; with 50 meters under floor tiles the search takes real time. Large data centers therefore often use locating cable systems that report a distance along the cable. With zone sensors, you get a similar result only by splitting the run into short, clearly named sections, such as one per cooling unit or rack row.
Data centers usually feed alarms into a building management system with redundant paths. Battery-powered wireless leak sensors suit retrofits, auxiliary rooms or colocation spaces there, but do not replace a hardwired system the operator’s design requires.
Also check the liquid. Milesight specifies the EM300 models for water and other conductive liquids. Some cooling loops run on low-conductivity treated water or glycol mixtures, so confirm with the manufacturer that your fluid will be detected.
Who receives a server room leak alert, and how fast?
The technology is rarely the slow part. A LoRaWAN leak sensor sends a message as soon as it detects a leak instead of waiting for the next regular interval. Via gateway, network server and platform, the notification typically goes out within seconds to a few minutes. Then comes the part many installations never plan: who reads it, and what if nobody responds?
Settle three things. First, the primary recipient, usually IT on-call, and after hours a named person rather than a shared mailbox. Second, escalation: if nobody acknowledges within ten to fifteen minutes, the alert goes to a second person, such as the building technician. Third, the channel. Nobody reads email at 3 a.m.; a text message, phone call or push notification with sound stands a better chance.
The message content decides the first minutes. Instead of a device ID like “EM300-ZLD-04”, it should read: “Server room, ground floor, leak below north wall air conditioner, 3:12 a.m.” A note on the first step helps too, such as where the chilled water shut-off valve is.
Distinguish delivered, acknowledged and resolved: an acknowledgment only means someone saw the alert, not that the floor is dry. By default, the Dragino WL03A-LB sends a confirmed message every ten minutes while a leak persists, which you can turn into a reminder for as long as it stays wet. A red dot on a dashboard is not an alarm system.
Does a wireless water leak detector work in a server room?
Usually yes, but verify it rather than assume it. Milesight quotes up to 2 kilometers in urban settings for LoRaWAN in the 868 MHz band, which assumes good conditions. A server room is often in the basement, behind concrete walls and a steel door, surrounded by metal racks. One gateway in the same building is usually still enough, but the margin shrinks.
Test from the final mounting position, not from your desk: trigger a message and check signal strength and signal-to-noise ratio on the network server. If reception is marginal, mounting the transmitter higher or closer to the door often helps. A weak signal also costs battery life: for the EM300, Milesight quotes more than ten years at SF7 with a ten-minute interval and 24 triggers per day, but only about 5.6 years at SF10 in EU868.
Easy to miss: where does the gateway get its internet connection? If it runs through a switch in the same server room, water damage can cut the very path the alert needs. Cellular backhaul or a connection outside the room avoids that shared dependency.
Both device families buffer data during outages: the EM300 stores up to 2,800 records and can retransmit them, and the WL03A-LB resends unacknowledged records once the network is back. That fills gaps in the history but does not replace a real-time alert.
What happens when a leak sensor stops reporting?
Many dashboards keep showing the last known state, usually “dry”. That is the most dangerous scenario in the installation, because a silent sensor looks exactly like a dry room. Server room water leak detection therefore needs its own rule for missing data.
The basis is the expected reporting interval. On the EM300 it is configurable, and Milesight’s battery figures assume ten minutes. The WL03A-LB sends data every two hours by default plus a device status every twelve hours. A common rule of thumb marks a sensor offline after two to three missed messages: about 30 minutes at a ten-minute interval, four to six hours at a two-hour interval. The offline alert goes to the same people as the leak alarm, possibly at lower priority.
If the gateway fails, every sensor goes quiet at once. A rule that watches the gateway and sends one combined alert is clearer than ten simultaneous alarms.
Test the whole chain regularly with real water, in a controlled way and away from live equipment. For the EM300-ZLD, a wet finger is not enough, because the manufacturer’s threshold requires at least 3 centimeters of wet cable. A shallow tray of tap water works more reliably. After a real leak: dry the cable, clean it with alcohol or soapy water if needed as Milesight recommends, and only treat the system as back to normal once the sensor reports “No Leak”.
Where can you buy water leak sensors for a server room?
The choice follows directly from your sketch. For a known, tightly confined source such as an air conditioner or a floor drain, a spot probe like the one on the Milesight EM300-SLD is enough. For pipe runs and equipment bases, you need a sensing cable, and there length decides: the standard cable on the Milesight EM300-ZLD covers 3 meters, while the Dragino WL03A-LB can be expanded with additional cables. Keep zones short enough that an alert names a place, because neither cable solution shows the exact leak point.
Check whether your liquid is conductive enough, whether the radio signal reliably arrives from the final mounting spot and how the reporting interval fits your offline rule. If you are looking for sensors for server room water leak detection, you can find our models in the leak sensors category.