Cecca - posted on facebook as well :
Akua Kolor waterbased inks by Rostow&Jung, non-toxic and easy clean-up with soap and water, can be used with dry paper -
check out their website:
www.waterbasedinks.com
I've been working almost exclusively with them for years, just recently began using oil based as I was experimenting with paper litho and etching.
Deeper, richer color with oil, but much more labor intensive and chemical involved, of course.
But, as you can see with some of my monoprints, you can achieve many layers and intense colors with water based as well.
Hope that helps