Water based inks are different from plastisol in that they use water to carry the pigment vs a plasticizer. Water based inks provide a softer feel as they absorb into the fabric more than plastisol. The downside is they are harder to work with and you do loose some opacity since water is the medium in which the pigments are carried. Because of this water based inks cost a little more. When used correctly the can be very eco-friendly. Steve Kahane wrote a great article in Impressions last year on this subject (http://impressions.issshows.com/screen-printing-process/Is-Water-Based-Ink-More-Eco-Friendly-Than-Plastisol-8724.shtml)