The following link may prove of some help (If you have overlooked it in the literature survey):

INFRARED REFLECTANCE SPECTROSCOPY FOR ESTIMATION OF MOISTURE OF WHOLE GRAIN

R.A STERMER, Y. Pomeranz and R.J.Macginty,

U.S.Grain Marketing Research Centre

Agricultral Research Service, U.S.

Department of Agriculture,

Manhattan,KS 66502.

Why do you want to determine water spectrophotometricaly ???? May seem ridiculously obvious but why not just dry it to constant weight ?

Dear Paul, thank you, but we find new reagent react with water quantitatively and gave deep colored species so it considered very sensitive spectrophotometrically

If you want to determine quantitatively then you can use Karl fischer Apparatus method for water,

For spectrophotometricaly, You can add the unhydrous CuSO4 which gives blue colour to the grind grains of rice and wheat, The blue colour intensity is depends on no of water moleculs. Then you can measure UV-Visible spectrophotometric method.