I can do it in 6.

Fill the 8 up. That's one move.

Pick the 5 up, and push it into the 8 cup, displacing 5 litres of water, leaving just 3. That doesn't count as a move because I'm not emptying, filling or pouring.

There's 3 litres left in the 8. Pour into the 10. That's 2 moves.

Repeat twice more.

I'm so fucking clever.