tub, washbasin
盥 centers on a container for water used in washing: a tub or washbasin.
盥 combines 水 (water) inside a container shape over 皿 (dish/basin), depicting a vessel for holding water. The exact historical development is uncertain, but the modern form clearly suggests a washbasin.
Water 水 is held inside a basin 皿, making a tub or washbasin for cleaning.
For カン, imagine a large can filled with water used as a washbasin: can -> カン.