Onset HOBO U20L Water Level Loggers

The Onset HOBO U20L is a low-cost, research-grade water level data logger for continuously measuring water levels and temperature in various underwater environments.


  • Available in 4 depth ranges
  • No-vent-tube design for easy and reliable deployment
  • Durable ceramic pressure sensor withstands freezing

The Onset HOBO U20L features 0.1% measurement accuracy, a polypropylene housing for fresh and saltwater use, and a non-vented design for convenient and hassle-free deployment.

Post-Purchase Add-ons
The Onset HOBO U20L data logger requires either the U-DTW-1 Waterproof Shuttle or the Base-U-4 Base Station for configuration and data offload, HOBOware software (free download).
*NOTE: HOBOware Pro is required when using the U-DTW-1 Waterproof Shuttle.


  • Freshwater
  • Saltwater
  • Including wells
  • Streams
  • Lakes
  • Wetlands
  • Tidal areas
Questions & Answers
Does the recommendation of using only 1 barometric reference logger for all water level loggers within a 15-mile radius apply to all ecosystems? Are there any recommendations for use in mountainous streams?
Since barometric pressure changes with altitude, loggers that are deployed at different elevations will require barometric compensation from a weather station or barometric pressure logger that is at the same altitude. The 15-mile radius (or 1000ft change in elevation) rule applies to sites that have loggers deployed at relatively the same altitude. If the elevation is drastically different at each site, it would be recommended to use a barometric pressure logger at that site, in addition to the level logger.
Are the batteries replaceable in the U20L series HOBO loggers?
While the batteries are replaceable, they are not user-replaceable and will need to be sent to the factory.
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