You can read this paper to know the action of PEG6000. Though this paper could not directly answered your question, it is somehow related with PEG6000 and water.
Simple, Rapid And Cost Effective Screening Method For Drought
Resistant Breeding In Pearl Millet
M.Govindaraj, P. Shanmugasundaram, P. Sumathi and AR. Muthiah
Electronic Journal of Plant Breeding, 1(4): 590- 599 (July 2010)