This novel application of ultrasonics doesn't really qualify as a sensor, but we wish we'd had it in place last week when our water pump quit (we have a spring-fed well). A bit of rust got loose in the pump casting and entered a little tube between the casting and the pump, resulting in low water pressure and a pump switch that ran and ran with each water draw until we shut it off by tapping it with a hammer. It seems the pressure sensor in the tube wasn't detecting an adequate amount of, well, pressure.
Oasis, from the British firm Waterite, is a nonintrusive ultrasonic water softening system that works without chemicals, salt, or filters. Environmentally friendly and easily installed, Oasis works by transmitting ultrasonic radio waves throughout the water system. These cause acoustic cavitation, which prevents calcium particles from attaching to pipe surfaces and joints, and pulverizes any existing calcium deposits. The system can reduce or completely remove chlorine, fluoride, and sulfur odors, as well as sulfates and iron discoloration.
The elimination of lime scale has numerous benefits for both commercial and domestic users. It helps to maintain the efficiency of water-heating systems and pump flow rates; reduces the need for regular strip-down and descaling; helps to prevent premature failure of plant and equipment; and prevents lime scale marks on taps and sinks. An additional benefit to softening water in this way is that the amount of detergent and cleaning chemicals is reduced by up to 30% in both domestic and commercial applications. The system is available in a range of sizes up to 15 x 15 x 8 in. It can be floor or wall-mounted, or fixed to objects or equipment, according to size and application. Installation is a straightforward matter of winding aerial wires around plastic or metal water pipes and connecting them to a mains. No plumbing, maintenance, or servicing is required and it is guaranteed for three years.