In this article a trip is taken to characterize concrete through its hardened cement paste based on its microstructure. Optical microscopy is coupled to advanced image analysis, as well as statistical data analysis to characterize heterogeneous concrete material. The article takes a closer look at the determination of the w/c ratio through the analysis of capillary porosity by using image analysis. It is shown that accurate analysis does not shown identical results in the w/c ratio even for standard reference samples with known w/c ratio. In the article it is shown that this is not because the techniques we use to determine the w/c ratios are not accurate enough, but much more because of the local variation in the microstructure. The attention shifts with this article from the analysis technique to what we actually observe in the microstructure. Hopefully this will change our thinking about the distribution in local microstructure variation and will help to set off more research towards the capturing and modelling of these local microstructure variation into consequences at a more structural level.@en