We have know for over a decade the importance of free-choice water for calves on an intensive milk feeding program. This does not,  however, mean that we cannot make mistakes.
 
Here is the situation. Summer and fall seasons go well for calves being fed 15 percent solids milk replacer. They begin at six quarts a day on 3X feeding. Over the first ten days the feeding rate goes up to ten quarts a day. Free-choice water and calf starter are offered. Low scours rate and good rates of growth. 
 
Now it is January. Cold housing - barn seldom more than 5 degrees warmer than outside. Sixteen of the last 30 days have had a night-time low below 10F. Milk replace feeding program is the same. That is,  27-20 milk replacer mixed at 15 percent solids.  Water freezes. Water is now only available for a few hours daily - some days not at all. Scours rate has increased among the younger calves.
 
Perhaps you recall that as the concentration of dissolved solids goes up in milk replacer the gastric emptying is progressively more rapid and complete. And, when water is not available the chances of clinical diarrhea often increase. In this case, we have arranged to change the milk replacer mixing rate down to 12.5 percent solids. We hope that reduction in osmolality [concentration of dissolved particles in a fluid] will make the availability of water less critical.
 
At the same time more effort will be made to provide warm water twice a day, especially for these younger calves.