This is kind of a general list.
The Flow meters you have already found: https://www.adafruit.com/products/833
You will also need a microprocessor of some sort. An Arduino UNO is ahbout the easiest one to program: http://www.adafruit.com/products/50
You will also need a power supply. This is a good one to start with: http://www.adafruit.com/products/63
The sample code for the flow meter works is written for the UNO and a basic LCD character display. http://www.adafruit.com/products/198
However, for multiple meters, you may want to go with a larger display such as this one: http://www.adafruit.com/products/498
The "backpack" simplifies display wiring and frees up pins for more sensors: http://www.adafruit.com/products/292
Since this is a pool application, You may also want to check out our range of waterproof enclosures, cables & connectors.