Lithium metal will burst into flame in contact with water, the same as potassium metal and sodium metal. Lithium compounds do not burst into flame in contact with water, just as potassium compounds and sodium compounds do not (e.g. sodium chloride – table salt).
I suppose de-ionised water does not conduct electricity but, if it can dissolve any of the battery chemicals, then it will conduct electricity. I don't think there is ever a situation where any kind of water is recommended for any kind of electrical fire. Maybe packing in dry ice (solid carbon dioxide) would be a safer way to cool.