Everyone has that one friend who never leaves home without their two-litre jug of water, and not surprisingly, this is usually the same friend who’s constantly looking for the nearest bathroom. But is this water-guzzling pal onto something? It’s no secret that drinking water is good (and necessary) for the health of runners and non-runners alike, but exactly how much water do we actually need? This answer will vary for everyone, but use these guidelines to determine if you’re staying hydrated.