Ya’akov’s words to his sons start with Reuven, whom he characterizes pachaz ka-mayim, 49;4. R. Samson Raphael Hirsch bemoans (really! you can look it up) the rarity of the root pachaz in Tanach, making it difficult to define/translate. From Shofetim 9;4’s using the word pochazim derogatorily when it described the people Avimelech hired to support him (along with reikim, empty), R. Hirsch assumes it is a negative, but is not sure what the negative is.
Upping our degree of difficulty, Ya’akov paired it with water, an item R. Hirsch finds too multiply meaningful to guide us here [he means water can symbolize Torah, life, and much more, not really easing our way to know what pachaz can mean]. Its most prominent characteristic, though, is its fluidity.
Sometimes that’s good, makes for greater flexibility. Here, R. Hirsch thinks pachaz takes a negative version, indicates a lack of stability. Water flows freely, takes on the shape of whatever container it is in, will overflow its borders. Reuven has that, Ya’akov was saying, but life requires us to have a solid core [to know when not to flow, not to just adopt what’s around us].
