There are two problems with adding energy boosters to the water in your hydration pack – they can stain the pack's bladder, and cause mold to grow in it. A couple of California-based entrepreneurs may have a solution, though, in the form of the HybriFlow system.
HybriFlow replaces the hose on most popular brands of hydration packs, and consists of a main unit that gets plugged into the bladder's water-output "port" (or whatever you want to call it), along with a cartridge that attaches to the side of that unit, and a hose that runs from the unit up to the user's mouth.
The hose, however, is actually a tube-within-a-tube. While the main tube only draws water directly from the bladder, a skinnier tube within it only draws liquid booster directly from the cartridge. Using a lever on the silicone bite valve, users can switch between sucking pure water straight through the main tube, sucking a mix of water and booster through both tubes at once, or simply shutting off the flow altogether.
The cartridge is reusable, and can be filled with a booster of the user's choice. Because that supplement is introduced downstream of the water supply, the bladder is left stain- and mold-free. Additionally, users still have the option of drinking straight water, which they wouldn't if they just added a booster directly into the bladder.
If you're interested in getting a HybriFlow system of your own, it's currently the subject of a Kickstarter campaign. A minimum pledge of US$29 will get you one, when and if they reach production. The planned retail price is $40.
You can see a demo of the system, in the video below.
And for another approach to adding boosters to hydration pack water – without gunking up the bladder – check out Infuze.
Sources: HybriFlow, Kickstarter