In sailplanes we add up to around 200 litres of water to wing tanks in single-seat gliders (empty weight typically around 280kg) to improve the high speed performance (typically up to 270 km/h these days) and ability to fly comfortably in turbulence.
It's surprising what you can fly formation with, even without an engine [1] :-)
[1] this particular glider does have a small engine for takeoff, but maximum speed with the engine extended is 180 km/h and here they are flying at 280 km/h.
Also from Stefan's channel, some fun here in New Zealand ... this flight passes just a couple of km from the Lord of the Rings "Weathertop" site (Google maps knows it).
