Dehydrated skin is something I find quite hard to understand and is definitely surrounded by a lot of myth and marketing.
This my understanding which might be wrong
Your skin can be dry, oily or combination. Dry skin is skin lacking in oil and much easier to spot.
Then your skin can also be hydrated or dehydrated as well i.e. lacking in water. The top layers of your skin are all dead cells that are dehydrating and eventually flaking off. This might be responsible for making your skin look dull or generally non-glowy AKA dehydrated. I am not convinced this just isn't normal skin and a way to make us buy more product but then I am bitter and twisted
This is why acid exfoliation makes you look better - it's revealing newer skin underneath. You can't actually hydrate these dead cells for example by drinking more water as why would your body put the water into cells it isn't interested in any more? Most of the publicity for drinking more water can be linked back to the bottled water industry 
So there are products claiming to improve hydration - these almost all contain hyaluronic acid. Hyaluronic acid is a massive molecule that isn't absorbed into your skin but it attracts water to it like crazy. So it sits on top of your skin and drags water into those dehydrated dead cells and may make your skin look better. If you have fine wrinkles it may even plump them up a bit so they disappear - it hasn't actually changed anything under your skin in the way a retinol would but on that day you've used it, it's made you look better.
Here's the thing - hyaluronic is in loads of beauty products and it's cheap. But I bought a tube of Hydraluron for £24 
when it's basically the same as Aldi Lacura serum for £3.49 
And there are masses of hydrating serums out now and unless they have other fanciness in, you might as well be buying the Aldi.
For me, as I already use an acid toner and Retin A and a moisturiser with hyaluronic in, I got nothing out of Hydraluron prob because my skin isn't dehydrated - but I still bought into the marketing. I do now use Hylamide but mainly for the peptide content.
So have a think about whether your skin really is dehydrated, or has some fine lines which you might like to try plumping out and also check if you have hyaluronic in any of your existing products, which you may well do 