Every two days should be fine. Tell them to be sure it is very wet when they are done watering, and they should not just sprinkle it lightly.
I bought a portable evaporative cooler, so the humidity in my growing space is usually around 70% now. It has made a huge difference to the plants. The device evaporates about 140 liters of water per day.
__________________ May the bridges I've burned light my way.