to exhaust, to drain dry
澌 centers on the idea of something being used up or completely emptied, especially of liquid: to exhaust or drain dry.
澌 combines 氵 (water) with 斯, which likely contributes the sound and the idea of dividing or cutting off, suggesting water being cut off or exhausted.
Water 氵 on the left and 斯 on the right: picture a stream being cut off and drained until nothing is left.
For シ, imagine a thirsty person seeing a drained river and sighing 'sheesh' in disappointment: sheesh -> シ, as the water is exhausted.