I use beer instead of water, and I slice up a large yellow onion and put that in the beer with the bratwurst, bring it to a boil, then let it simmer for about ten minutes. Then I grill the brats, place them in toasted buns, top them with a hot horseradish and then add the beer-boiled onions.
Try this: place brats in large skillet of boiling water with one tablespoon spicy brown mustard and sliced onions. Cover and simmer until liquid reduces, add green pepper rings and let simmer until green peppers are done but not overdone. Place brat, onions and green peppers with a bit of the thickened potliquor on bun and cover with a sprinkling of crispy fried bacon.