Peel, seed and cut squash into 1/2 inch cubes.
Combine water, sugar, vinegar, turmeric, ginger, salt and dry mustard in a large sauce pot.
Bring mixture to a boil.
Add squash and onions; boil 10 minutes.
Pack hot into hot jars, leaving 1/4 inch head space.
Process 10 minutes in boiling water bath.