I have lupus and a water pill caused me to have less pain. why is that?

Less swelling: The water pill may be making your tissues, joints, etc less swollen, and this may reduce pain.

Uncertain : Although this is not likely association, it is not clear what type of pain was improved. People that have variety of different types of pain, and the question might be more easily answered if we know exactly which pain you're having. We do not usually think of water pills causing pain relief.