It is meant for water and has the following models:
3000L/H 10W, 3600l/h 20W, 4500l/h 30W, 5200l/h 40W, 7000l/h 50W, 8000l/h 70W, 10000l/h 80W, 12000l/h 100W
Which one would be enough?
What about water cooling? Would 6 liters/second be enough?
I would not recommend using a water pump for an air assist. Not sure if it would even put out air (that one seems to be an impeller drive, so no air), but would defiently overheat. Using a large aquarium/pond air pump is what a lot of people use. Some also use a standard air compressor or even airbrush compressors. Typically you want at least 10 L/min airflow, but also depends on what type of air assist nozzle you are using.
For water cooling you want at least 40L/min as a minimum.
The ratings of these pumps are 4 nothing hooked up to water outlet, by hooking up 6mm hose cuts flow by 90%, I used a 150 watt pump that pumps 2 liters per minute when connected to laser tubes,