Running out of water at a remote campsite is a mistake you only make once. Water monitoring systems tell you exactly how much water you have left in your fresh, grey, and black water tanks, so you can plan refills and manage consumption rather than guessing. If your caravan doesn’t have a tank monitor (or has one that doesn’t work reliably), adding one is a cheap, high-impact upgrade.
Types of Water Monitors
Probe-style (resistive) sensors: The most common factory-fitted option. Metal probes inside the tank measure water level at set points (typically ¼, ½, ¾, full). Cheap and simple, but notorious for inaccuracy as probes corrode, get coated with mineral deposits, or give false readings. If your factory-fitted level gauge seems unreliable, this is probably why.
Ultrasonic/non-contact sensors: Mount externally on the tank (no contact with water). Use ultrasonic pulses to measure distance to the water surface. Far more accurate and reliable than probes because nothing corrodes or fouls. The Gobius or similar sensors give continuous level readings rather than just ¼ increments. Around $100 to $250 per tank.
Pressure-based sensors: Measure water pressure at the bottom of the tank, which increases proportionally with water depth. Accurate and reliable. Some require a fitting to be installed in the tank; others clamp externally. Around $80 to $200 per tank.
App-based systems: Modern monitors like the Gobius or RV Whisper connect via Bluetooth to your phone, giving you tank levels at a glance on an app. Convenient but dependent on phone battery and Bluetooth range.
Our Recommendations
| Product | Price (per tank) | Type | Best For |
|---|---|---|---|
| Mopeka Pro Water Sensor Best Pick | $80–$120 | Ultrasonic, Bluetooth | Best value, integrates with Victron/Simarine |
| Gobius 4 | $150–$220 | Ultrasonic, Bluetooth | Accuracy, easy install, no tank penetration |
| BM Pro BatteryPlus35 | $350–$450 (system) | Pressure sensor, panel display | Combined battery + water monitoring |
| Simarine Pico | $400–$500 (system) | Ultrasonic, touchscreen | Premium all-in-one (water, battery, solar, gas) |
| RV Whisper | $200–$300 (multi-tank) | Ultrasonic, app-based | Comprehensive monitoring (water + power) |
Detailed Breakdown
Mopeka Pro Water Tank Sensor ($80 to $120 per sensor): Our top pick for most caravanners. Ultrasonic sensor that sticks to the bottom of polyethylene tanks with no drilling. Connects via Bluetooth to the free Mopeka app, and integrates directly with Victron GX devices and Simarine displays. If you already use Mopeka for gas bottle monitoring, the water sensors use the same app. Best bang for buck on the market.
Gobius 4 ($150 to $220 per sensor): A well-established non-contact sensor that mounts externally. Accurate percentage readings via Bluetooth app. Slightly more expensive than Mopeka but very well-proven and available from most Australian caravan accessory stores. Good choice if you want a standalone system without needing Victron or Simarine integration.
BM Pro BatteryPlus35 ($350 to $450 for the system): Australian-made combined battery and water tank monitor. Shows both battery state of charge and water tank levels on a single panel display. Good for people who want one unit covering both systems. Pressure-based water sensing is reliable and accurate.
Simarine Pico ($400 to $500 for the system): The premium option. A sleek touchscreen that monitors water tanks, battery, solar input, and temperature. Supports multiple tank sensors. Expensive, but if you want one beautiful display that shows everything, this is the one. Very popular in high-end builds and van conversions.
If your factory-fitted water level gauge is unreliable (and many are), retrofit an ultrasonic sensor rather than trying to fix the probes. External-mount sensors are easier to install, more accurate, and don’t corrode.
- Ultrasonic/non-contact sensors are far more reliable than factory-fitted probe-style monitors.
- A Gobius 4 ($150 to $220 per tank) provides accurate, corrosion-free monitoring with Bluetooth app integration.
- Knowing your exact water level prevents running dry and helps you plan refill stops.
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