Relative to vacuum cleaners, water lift is a measurement of the strength of the vacuum produced by the suction motor. Suction gauges used on vacuum cleaners are calibrated in "Inches of Water Lift". This is equivalent to taking a vertical tube, placing the bottom in a container of water, attaching the vacuum cleaner hose at the top and measuring how high above the water surface the water in the tube rises. By the way, one cubic inch of water weighs 0.036 pounds so the negative pressure in pounds per square inch can be found by multiplying the water lift by 0.036. If you see suction rated in millibars (mbar), mulitply that number by 0.4 to convert it to inches of water lift.
also the higher above sea level the better the water lift