Carrying water bottles on the fork is standard bikepacking practice, and is familiar from touring bikes going well back. (My friend Ed Carman’s beautiful mid-1970′s Eisentrout Limited has a fork that is probably not the original but was drilled for bottle mounts in the early 80′s). I’ve secured two bottles to each fork leg with no grief.
I have also used Salsa’s Anything Cage to good effect on my forks, secured by a combination of hose clamps and the mid-fork rack mount. As long as the loads are kept reasonable and are roughly symmetrical, bike handling is only minimally affected. The concept is exemplary, but Anything Cages are fairly fragile. Salsa has promised a redesign.
Jeremy at Cleaveland Mountaineering sews up an alternative in the form of a cordura semi pocket with a closed bottom and a metal stiffener to bolt to triple bosses. Optional large steel band clamps are available for attaching it to an undrilled fork. The pocket has two straps with metal strap locks to secure diverse roughly cylindrical loads. Because the body of the pocket is soft and compliant, there isn’t a chance of damaging it from rough road shaking or laying the bike down. The pockets each weigh a bit more than an Anything Cage, so this is not a weight saving measure. Still, the bomber construction, ease of use and massive versatility absolutely gets the job done.