[raybbr]

They mandate MTBE in gasoline to reduce emissions, but then contaminates millions of gallons of potable water.

MTBE is no longer used. Hasn't been for almost a decade.

From what I understand MTBE is a by product of gasoline production and is costly to get rid of. The oil companies convinced the "greens" that adding it to gas would be better for the environment.

[Doulos1]

Not exactly, according to others.
http://mises.org/daily/401/