We present a microscopic description of the vibrational spectroscopy of the OH stretch of HOD in liquid D2O, Our model predicts that OH frequency correlations decay with a sharp and rapid (approximate to 35 fs) decrease, followed by a beat at approximate to 125 fs from intermolecular oxygen vibrations. On a short time scale (approximate to 200 fs), ultrafast infrared spectroscopy of the OH stretch is sensitive to localized intermolecular motions. For times longer than approximate to 200 fs, cooperative molecular rearrangements drive dephasing. The interplay of electric field fluctuations, both local and cooperative, dictate vibrational frequency shifts and destroy vibrational coherence in water.