Before you load up on potassium... are you sodium depleting?
I know you are getting a lot of different answers, but there is another consideration that might be the problem. It is often over looked. The symptoms of low sodium and low potassium are very similar. This is why people get confused to which one to add. When you get muscle cramps, people automatically think to they need more potassium when they may need more sodium or reduce their potassium intake.
You are not taking in very much sodium. Your water intake is very high, so your body is not retaining water. When you are training, you are losing more water and sodium by sweating. Most of the time you are eating meats, white, red and/ sweet potatoes and other foods that are very high in potassium. Your multi-vitamin also contains potassium. This is how Your sodium gets too low and your potassium gets too high. The best way to correct the imbalance is to reduce potassium intake.
This happened to me before a competition. Someone told me to add potassium to stop the cramping. The cramping actually got worse. When I asked my diet coach about it, she told me about the dangers of too much potassium. She crashed during a competition and ended up in the hospital from too much potassium. Once I changed my diet a little... it went away.
Anyway... it's just a consideration. Hope it helps.