Today I dived into a river that was a touch over 50 degrees fahrenheit, 10 centigrade. I did three different dives for only about 10-second immersions each. I feel like I am becoming more cold adapted.
CWI might even have a strong placebo effect, which means in essence you are fooling yourself into a healthy state (better than deluding yourself into an ill state!).
So how do you motivate yourself to do it?
Keep personal records, your P.R.: Keep track of the coldest water you ever dived into, or the longest time you spent in water less than 60 F. or 15 C., so that it becomes an internal competition, a self challenge. This is human nature; the longest you ever swam, the tallest mountain you hiked, the longest you ever threw a frizbee, etc. This factor may appeal to more competitive personality types, but everyone has used the technique of setting or seeking a memorable goal as the simplest form of motivation. Keep a diary or log of your cold-water swims and dive-ins.
I have a kind of index that I track that combines the ambient air temperature with the water temperature. For example, my record is 100 for the combined cold-water immersion and air temperature (which involved diving into 50 degree waters when the air was 50 F., too). It's another P.R. that you can track. for example, today was a sunny 59, and the water was just over 50, making it a 109-110.
Notify your tribe. Share what you did with your friends and fellow CW swim fanatics or health buffs, such as via email or Twitter. This gives the event more meaning to you than internal gratification, and can motivate others to choose a new healthy activity.
Along the same lines, join a cold water swim or "polar plunge" club, which makes CWI more of a fun social event. It also makes it less likely that you dip your feet in the water and do the old 180 ("Not today…").