Cr(acac)3 works every well in organic solvents for speeding up T1 relaxation, but does not dissolve in water.  A good choice of water soluble T1 relaxation agent is GdCl3.  Recommended concentration is 0.1-0.3 mg/ml.

This method is also good for water-swellable solid samples – prepare a GdCl3 solution and swell your polymer sample in the solution, and you have finally found a solution to your challenging signal intensity problem!