Whisk together the dry mustard, brown sugar, salt, turmeric, paprika, and garlic powder in a small, microwave-safe bowl. Measure out the pickle juice, water, and vinegar and have standing by.
Place the mustard seed into a spice grinder and grind for a minimum of 1 minute, stopping to pulse occasionally. Once ground, immediately add the mustard to the bowl with the spices and pour over the liquid mixture. Whisk to combine.
Place the bowl into the microwave and heat on high for 1 minute. Remove and puree with an immersion blenderfor one minute. Pour into a glass jar or container and cool uncovered. Once cool, cover, and store in the refrigerator for up to 1 month.