Gallons (UK) to tons (water) conversion calculator above calculates how many tons (water) are in 'X' gallons (UK) (where 'X' is the number of gallons (UK) to convert to tons (water)). In order to convert a value from gallons (UK) to tons (water) simply type the number of gal to be converted to tons (water) and then click on the 'convert' button.