Water based functional fluids

A functional fluid composition for use as a hydraulic fluid, lubricant, cutting fluid or drilling fluid which comprises (a) from 20 to 98% by weight water (b) from 0 to 80% by weight of a glycol, and (c) from 0.5 to 25% by weight of a thickening agent prepared by (a) reacting one mole of a monofunctional active-hydrogen-containing compound having at least 10 carbon atoms with between 20 and 400 moles of one or more alkylene oxides and (b) thereafter reacting the product of step (a) with a diepoxide in an amount such that the molar ratio of diepoxide to hydroxyl groups in the product of step (a) is between 0.2:1 and 5:1. The fluid may further comprise functional components for preventing wear and corrosion and also 0.5 to 15% by weight of a non-ionic, cationic, anionic or amphoteric surfactant. i