Water injection used on the B707-100 series powered with JT3C-6 engines used 400 gallons of de-mineralized water in 2.5 minutes at takeoff power, which ran the tank dry...so no problem with freezing at altitude. This water injection supplied an extra 2000 pounds of thrust per engine, as I recall...been a long time ago. These aeroplanes (some anyway) were later fitted with JT3D-3B engines (fan) which eliminated the need for water. Also MUCH quieter...for the airport neighbors anyway.