Manual says: "Use only windshield washer fluid meant for automotive vehicles. Using other substances, such as untreated water, can result in bacterial growth within the climate control system resulting in odor or potential damage that is not covered by warranty. Do not add formulated washer fluids that contain water repellent or bug wash. These fluids can cause streaking, smearing, and squeaking or other noises. In temperatures below 4° C, use a washer fluid with antifreeze. In cold weather, using a washer fluid without antifreeze can impair visibility through the windshield."
I use Toyota Washer Fluid. I also thought the BMW washer fluid was really good. I do know that most dealership service folks use the blue stuff from Walmart or wherever. This may be better than water, but have never been satisfied with the results.