Quail don't bath in water (they are unable to regulate their temperature when wet), so instead, they bathe in dirt, sand or even food!
I'd suggest putting a small box filled with sand or soil for them to dust bathe in as it helps keep their feathers clean and mite-free (and probably dander free as well, I presume). If you're planning on giving them soil from your garden, I'd also suggest you worm the quail as a precaution as no one can tell whats hidden in the dirt. You could also use diatomaceous earth, a better alternative to soil. The only problem is that when they dust bathe, dirt and dust flies everywhere into food, water, and outside the cage so take that into consideration.
Before I used chicken nipple waterers, I just had a regular container for their waterer and would refill it daily, but when my quail started to dust bathe, they'd get their water dirty so easily, so I moved the cage to a grassy area with no soil so they can't dust bathe, and then I'd take them out of their cages regularly to dust bathe in a patch of soil nearby. They aren't flighty, so I know they won't fly away from me. However, I don't have to do that again anymore thankfully. ^^
Good luck!