Assumming that the pump starts at a certain pressure, either or a combination of the following indirect measurements might work. After the motor inrush current and interia of the column are past: 1. measure the current drawn by the motor, 2. measure the flow rate.
Of course there is the problem...
The ARRL Handbook (hams still do hardware---sometimes) is published yearly and has distilled information on rf circuits and techniques.
Still one of the best desert island books on electronics.
Any library has one--my first exposure to hamming was a 1948 edition in the high school library...
