Hmm, I don't think I'm qualified to answer this question but sometimes I can't help myself
This seems to be a burning issue for many people which I can't understand. If you weighed 200+ kilos or more, perhaps I could understand your question a little more but I truly find this question puzzling. I guess we all have different reasons for wanting to lose weight and appearance is important and I agree - that is important to me too. But, more importantly to me, is the health benefits. But that aside, back to your question.
I don't think there is anything you can do against "saggy" skin. I don't think I have any but then again, I haven't checked carefully. I have been as heavy has 127kg and now I weigh a bit over 95 kgs - I think I still look the same - no skin anywhere. I'm fairly sure nothing in a bottle can do anything for skin (or saggy skin) other than sunscreen. I'm sure water helps for skin health overall but not against 'sagging' I shouldn't think.
My only understanding about this issue is that sagging skin has to do with the elasticity in your skin which decreases with age and/or hormonal levels and not much else but I'm not a doctor I have absolutely no qualifications whatsoever to answer this question - just an opinion.
For me, losing the weight and being healthy is a much better option that remaining overweight and obese, saggy skin or not. Given you haven't got that much weight to lose, I don't think you'll have a problem if that was want you were wondering.
Hope I've helped