My take is since you have been running for some time now, you do not have to abandon your speed to take on the half marathon distance. My suggestion is for you to visit the McMillan Running Calculator (see link below) which will help you determine a good training pace for your LSD runs, intervals, tempos, etc--Also, find a good training program that takes you from where you are right now to where you want to be--in other words, if you are consistently running 5-7 miles for your LSD runs you don't want to start with a training program that begins your LSD runs in the 3 mile range.www.mcmillanrunning.com/
As for water, this is far more important than a fueling source. Either locate a trail with water fountains or bring some with you. As to how much you need will vary according to the ambient temp, the humidity, your sweat rate, radiant heat etc.
As for what is a long run in half-marathon terms--it's generally the longest run of the week--which once again will vary according to your training program.
Injuries happen even to the best of us--in fact 80% of all runners will experience at least one injury in their running career. While many runners blame injuries on their shoes, lack of fueling, etc...know that many injuries are caused from not allowing enough recovery between your runs AND not building the ancillary muscles of the hips to support running. Below is a link to my running coach's exercises he has me do every run.www.youtube.com/watch?v=2GLrKr54yA0
I hope this helps! HAPPY RUNNING!
ACE Certified Personal Trainer, RRCA Certified Running Coach
Member of the NTX Runners, DRC, Rockwall Running Club, Plano Pacers, NYRR, Team Runnersconnect
"No weight is ever PERFECT enough to do the enormous job of CREATING happiness!" From The Don't Diet, Live-it Workbook