Based on the limited requirements you describe this is how I would design the system.
I would use a pair of flow regulators to introduce the two liquids together at the correct ratio in-line. In your example I would run the coolant at (0.5)Liter/UnitTime and the water at (49.5)Liter/UnitTime. As long as the two liquids are being dispensed over the same UnitTime you wont need an additional reservoir.
I would then run the two liquids through a shear mixer. These are common in LSR(Liquid Silicone Rubber) injection molding for homogenizing colorant and multipart liquid silicone prior to the injection barrel.
Here is just the first link I pulled up for shear mixers online just so you have some reference.
From there the system can be coupled to whatever you need downstream. Best of luck!