A water-dilutable, microemulsion concentrate of slow-burning hydraulic fluid intended for use in underground mining headers, hydraulics for powered roof supports, hydraulic stands and other machines and equipment used in water hydraulics. It gives the hydraulic system the required lubrication, biological stability and anti-corrosive protection. It contains 30% of highly refined mineral oil, emulsifiers, synthetic lubricants and biocide additives, corrosion inhibitors, anti-scaling agents and water (>15%). It is used as a 0.5 – 5% hydro microemulsion.