Do you think Fullers when you think ESB? If that is the case, they use London's water utility water and add gypsum to get the Ca and SO4 up. They say that on the tour, and you can see the bags of gypsum by the HLT. What they don't say is the level they get the SO4 to. IIRC John Keeling says to get he Ca to 100 ppm.