Copper (I) hydroxide, CuOH, has been studied since the early 20th century, with inconclusive results. The material occurs at the surface of metallic copper immersed in water, but the solid form is poorly characterised. A yellow compound that is believed to be CuOH may be obtained by a variety of routes, the simplest of which is the reduction a Cu(II) salt by ferrous sulfate in the presence of disodium ethylenediamine tetraacetate. The infrared spectrum clearly shows the presence of water, making comparison to calculated spectra of the material uncertain. In order to characterise the material, it is essential to understand the role of water in the yellow product. Is it a structural component i.e. lattice water? Or is it present “adventitiously” as a shell to a core of CuOH? INS spectroscopy using TOSCA should answer this question.