The short version
Flasks for racing, a bladder for long unsupported days. Front flasks let you see exactly how much you have drunk, refill in seconds at an aid station, and mix different drinks in each. A bladder carries more water in less bulk and puts the weight on your back, and it hides how much you have left, which is exactly the information you want in heat. Many people run both: flasks in front, bladder in back for the long carries.
Common questions
How much should I drink per hour?
It depends on heat, effort and your own sweat rate, so work out your own rather than following a number. Weigh yourself before and after a long run in typical conditions to estimate loss. Drink to thirst rather than to a schedule.
What about hyponatremia?
Dangerously low blood sodium, and in endurance events it is more often caused by drinking too much plain water than too little. It is a medical emergency and it has killed runners. Take electrolytes on long efforts, do not force fluid beyond thirst, and get medical help if someone becomes confused, nauseated and puffy late in a race.
How do I stop a bladder tasting stale?
Rinse after every use, dry it fully with a hanger or a rolled towel inside, and freeze it between uses if it will sit for a while. Sugary drink in a bladder is what causes most of the problem, which is another argument for keeping mix in a flask.
At a glance
| Osprey Hydraulics LT 1.5L Reservoir | HydraPak SoftFlask 500ml, 2-pack | |
|---|---|---|
| Capacity | 1.5 litres in one unit | 500ml each, usually two |
| See how much is left | No | Yes |
| Refill speed at an aid station | Slow, vest off | Fast, in place |
| Separate drinks | No | Yes, one plain and one mix |
| Cleaning | Fiddly, needs drying | Easy |
| Weight distribution | On the back | On the chest |
Choose the Osprey Hydraulics LT 1.5L Reservoir if…
You are out for hours between water sources and capacity is the constraint. A bladder carries more without turning the front of your vest into a wall of bottles, and the hose means you sip without breaking stride. Accept the trade: you will not know you are running low until you suck air, which in heat is the wrong moment to find out.
Check Osprey Hydraulics LT 1.5L Reservoir on Amazon
Choose the HydraPak SoftFlask 500ml, 2-pack if…
You race, or you want to know what you are drinking. Two front flasks are the standard setup for a reason: you can see the level, refill without taking the vest off, and keep electrolyte mix in one and plain water in the other. That last point matters more than it sounds, because sugary mix is a poor choice for washing down a gel.
Check HydraPak SoftFlask 500ml, 2-pack on Amazon
Full reviews of vests for each approach
The Osprey Duro 15L includes a 2.5 litre reservoir in the box, while the Salomon Adv Skin 12 ships with two front flasks and takes a bladder as an option. Both reviews cover how each one refills at an aid station.
Related
Comparison based on published manufacturer specifications and the general consensus of owner reports. We have not tested these products side by side. Confirm current specifications and prices before buying. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.