A method of making a phosphono-phosphate compound is disclosed. The method involves a first step of mixing a first component comprising a phosphonic acid, a phosphonate or mixtures thereof, with a second component comprising a source of phosphoric acid or phosphate. The mixture has a molar phosphorous ratio of the first component to the second component of from 1:1 to 1:10. The second step involves either physically or chemically dehydrating the mixture to produce a phosphono-phosphate compound.
