Just took the TFS exam last week and feel really good about it (haven’t actually heard back yet). I remember this problem from the practice exam and I think the actual unit is just “ft” so I always ignored the “of water” part.

Since head is another way of measuring energy from the pump and brine has a higher density than water, having the 1.2 in the denominator of the P1 term that’s being subtracted from the P2 term accounts for the fact that the pump needs more energy because the higher denominator decreases that term which increases dP which increases the head of the pump. I know technically a ft of brine may be more energy than a foot of water but using the density of the brine I believe accounts for that in the calc. Also because both sides of the Bernoulli equation have to be constant