Pour the mustard into a medium pan. Fill the mustard jar with the vinegar. Place the lid on it and shake it up to capture all the mustard left in the jar.
Cut the stems from the peppers and quickly cut them into chunks. Place the chunks of pepper into a food processor and add the vinegar from the mustard jar a little at a time while processing the peppers. Process until well blended.
Pour it all in the pot with the mustard, sugar, and salt. Bring it to a boil for about 5 minutes.
While the mustard is cooking, mix the water and flour together and have it ready.
Turn off heat and add flour mixture. Put into jars. Process for 20 minutes.