H1MU stands for "high-μ", where μ is a ratio of uranium and lead isotopes (μ = 238U/234Pb). The fifth component is depleted MORB (DMM).[21] Because the behavior of water is very similar to that of the element cesium, ratios of water to cesium are often used to estimate the concentration of water in regions that are sources for the components.[2] Multiple studies put the water content of FOZO at around 0.075 wt%, and much of this water is likely "juvenile" water acquired during the accretion of Earth.