Here's what other sites are saying:
Cylindrical shape requires no special mouth orientation. Unique mechanism delivers full flow with just a soft bite. Will not leak even under pressure or with prolonged use. Build-in bayonet style shut off.
The Source Helix Valve provides an upgrade to the bite valve on your Source hydration pack.
Source Storm Valve Kit
Source Valve Docking Station
Source Helix Tube Kit
Guyot Designs SplashGuard
Nalgene Insulated Water Bottle Sleeve
CamelBak Fresh Reservoir Filter
$15 - $19
MSR SweetWater Prefilter
$1 - $9