Water access is fundamental to poultry welfare, with dehydration causing rapid physiological stress and welfare compromise. Broilers and laying hens require 1.5-2 times their feed intake as water; impaired access reduces growth, egg production, and immune function. Drinker type significantly affects welfare: nipple drinkers provide cleaner water but require birds to reach appropriate trigger pressure; bell drinkers allow open-water access more naturally but accumulate pathogens. Research demonstrates that broilers preferred open-water drinking systems when given choice, spending more time drinking and showing lower stress indicators. Water height and pressure adjustment is critical as birds grow; incorrect calibration causes chronic thirst. During heat stress, water intake increases 3-4 fold - failure to maintain adequate flow causes welfare emergencies. Medicated water delivery (antibiotics, vaccines) requires careful calibration to ensure therapeutic doses without restricting access. Farm welfare audits include water access as a Tier 1 outcome measure.