  We reduce the dimensionless interaction strength in graphene by adding a
water overlayer in ultra-high vacuum, thereby increasing dielectric screening.
The mobility limited by long-range impurity scattering is increased over 30
percent, due to the background dielectric constant enhancement leading to
reduced interaction of electrons with charged impurities. However, the
carrier-density-independent conductivity due to short range impurities is
decreased by almost 40 percent, due to reduced screening of the impurity
potential by conduction electrons. The minimum conductivity is nearly
unchanged, due to canceling contributions from the electron/hole puddle density
and long-range impurity mobility. Experimental data are compared with
theoretical predictions with excellent agreement.
