Your hair is made to REPEL water! Your hair is enclosed by a hydrophobic (water hating) layer, this layer repels water so that the hair doesn’t absorb too much water because water makes the hair weak which can lead to breakage. When you over brush or heat style too much (e.g your hair gets damaged) this hydrophobic layer is being damaged/removed. The hair feels brittle/rough and doesn’t repel water well anymore. As a consequence the hair absorbs water more easily (something you don’t want). That’s why, when you dry your hair, the ends dry less easily than the roots because they are more damages and thus absorb more water. So the idea of putting water on your hair e.g litteraty hydrating the hair does not make sense. What you do want is to renforce this hydrophobic layer or protect it. Just to take an example (absolutely not sponsored): that video from dreamcoat that went pretty viral, where the serum is applied and a drop of water is then applied to the hair, which is then bounced off. This perfectly shows that such serums help to protect or even re-enforce that hydrophobic layer. Extra note: Some times hair porosity is explained as the ability of your hair to absorb moisture and maintain moisture. I prefer to explain porosity as hair damage but it could also be explained in terms of water absorption because damaged hair (so the hydrophobic layer is damaged) doesn’t repel water well and absorbs water. - So high porosity hair is very damaged hair with cracks in the surface layer of the hair where water will be absorbed. High porous hair well therefore sink more easily in water because it absorbs water more easily. But this just means that your hair is damaged (something you don’t want). -Low porous hair is not damaged and repels water well. As simple as that.