This post is about the PMC Versaline VL2111 – WLS-31 Water Level Datalogger. This looks much like the Global Water WL-16, but instead of a silicon bladder at the end of sensor, it has a non-fouling ceramic sensor. At $1,370 before tax and shipping, it has a higher purchase cost than some alternatives, but it is my recommendation for durability, reliability, and low maintenance.
The Versaline is made for wastewater; in other words, for sewer lines. The datalogger end is vented and it is not supposed to be submerged. However, it is made to put inside manholes where it is very warm and humid. The PMC guys have maintained the sensor end in rough environments with the equipment lasting 8 to 12 years. If the sensor gets completely covered with algae (or something worse), it still works. It can be cleaned off with a toothbrush if it seems so clogged it might prevent water from getting to the ceramic end. The data logger and sensor are fairly new but are improvements on the older, long-lived versions.
The VL2111 – WLS-31 is three times the cost of the least-expensive option that I have seen so far. However, it might be the least expensive in the long run…it sure is the most worry-free of all the options listed here!