I have said elsewhere, but will say it again here – I am not at all sure that suet pellets are good for hedgehogs and have not seen them recommended anywhere, officially, for hedgehogs. They are actually designed for birds. I can’t help thinking that a balanced diet, i.e. in the form of hedgehog food has got to be better for them. We don’t want to end up having a problem with obese hedgehogs from eating too much fat!
I am not sure from your post whether you are feeding something else as well as the mealworms. If not, then mealworms should only be a very small snack and not the major part of the food you put out. You may have seen from the above posts on this topic that, although the hedgehogs do love them, mealworms not do not have very good nutritional value for them. It is better to offer them either one of the many hedgehog foods which are available, or cat/dog food – meat varieties – and preferably in jelly not gravy or cat/kitten biscuits – not fish varieties of any of these. This will make for healthier hedgehogs. A few mealworms is ok, but not too many. As you say, fresh water is always important. They do seem to drink a lot and rely on us for that, particularly when the weather is dry.
Good luck with the hedgehogs.