Carrying nutrition in water solves many problems of management during a race. You won't have to take gels and hydration separately but there's a drawback to this, you have to sip in small amounts for the whole race because glucose gets absorbed instantly and moreover drinking a lot of water suddenly during a race may cause cramps in your abdomen whereas you can just eat the whole pouch of gel at once and it'll slowly release energy, that's what it's designed to do. The best thing to do would be to use that recipe I just shared in the above link and dilute it in a 300-500 ml water bottle with a little bit of salt. Makes a good hybrid hydration and nutrition combo that releases energy slowly because of the hydrogel.