Drinking fluids routinely every day is an important habit for any athlete.
Adults should consume 2 – 3 liters each day (scale this down to fit your needs if you are on the smaller side ( a north American adult I 177lbs).
Consuming a sports drink during and after a shorter run like 2 - to 5 km will help replace salts and sugars that are lost during your run.
Lemonade coloured urine suggests good hydration. Dark urine, feeling unusually fatigued or leg cramps mean you are not adequately hydrated. A good reference is the Registered Dietitians of Canada
Review the signs of heat exhaustion prior to the season http://www.redcross.ca/who-we-are/newsroom/news-releases/archives/2012/beat-the-heat-and-stay-safe
Remember that it is possible to drink too much water (Hyponatremia) . The symptoms are similar to heat exhaustion.
Adjust fluid intake and vigilance for heat exhaustion by consulting the heat index prior to activity.