Our well water tastes very good but is extremely hard (220 mg/L). Do I need to make any adjustments when cooking or baking or will it work fine? 
If all you're doing is taking clean dry recycled cans, and filling them with food for immediate consumption I can't see there's any food safety problem at all. The can  contents would have been  commercially sterile when purchased and the tin plate and laquer are reasonably robust - any undamaged surfaces must be suitable for food contact. Watch out for sharp edges, tho'. 