On July 22nd between 7:30-7:45 pm 23.0 mm of rain fell.
That is the highest 15 minute rainfall we have recorded in the 10 year history of the UW weather station.
The previous record was 16.2 mm on June 27, 1999.
We also set an hourly record with 34.4 mm coming down between 7:15-8:15 pm.
That just surpassed the 33.9 mm on May 2, 2000.
By the way, I don't know how far back these records go, as they don't keep 15 minute data at the Waterloo-Wellington airport and I don't have their hourly data.
Not a record, but also interesting is that the temperature dropped 6.2°C between 7:15-7:45 pm.
On a personal note I happened to be biking just as the storm hit (I really should have checked the radar before I left) so I ended up watching the record rainfall from the (partial) shelter of one of the RIM buildings.