A horse that refuses water crossings is one of the most common practical challenges in backcountry packing, and the approach to resolving it must be appropriate for the horse's specific reason for refusing — genuine fear, a learned avoidance response from a previous bad experience, or simply the horse's test of whether the handler will be consistent in asking.
For a genuinely fearful horse, the most effective approach is desensitization that begins far below the threshold of the actual problem. Introduce water contact at home — a garden hose on the feet, walking through a puddle, standing on wet ground — and work progressively toward deeper and moving water before the trip. Attempting to force a truly fearful horse across a stream in the backcountry by brute pressure typically produces a scrambling, panicked crossing that reinforces the fear.
For a horse that understands water but is testing the handler in a specific situation, consistent pressure and release — asking forward with leg and rein, releasing the moment any forward movement occurs, and building on that — is appropriate. Following a calm, water-confident horse across is highly effective, as horses are social animals that take confidence from companions. Having another horse walk calmly into the water first while the resistant horse watches often resolves the initial hesitation without a confrontation.