There is a bad smell coming from my toilet water. This is in only one toilet in house. It still flushes, but all of the water does not flush each time.

Incomplete flushes can be caused by several things. Was there any work done on this toilet that may have made matters worse like a new wax ring? If not start by checking the tank, adjust the float so the water reaches a 1/2" below the top of the overflow tube. Back to you

The toilet has not been worked on can you think of whatelse besides the wax ring needing replaced.

I have one that most repair plumbers miss.. Look down at the bottom of the bowl. If there is a small hole, then that is a jet that starts the syphon action. If it's clogged the water will just swirl around and slowly go down leaving solids behind. Take your finger,(UGH! ) and run it around the inside of the opening. Over the years minerals build up and cut down on the syphon (flush) action. If it is rough or you feel build up, take a table knife and put a bend in it to get around the curve in the bowl and chip and scrap it clear. Next take a coathanger and clear out the holes around the rim. They start the swirling action. And last, check the water level in the tank. It should be 1/2" below the top of the over flow tube. And speaking of the overflow tube, Make sure the small 1/8" tube from the ballcock to the white overflow tube is connected so it discharges in it and that it's flowing when the ballcock fills. This is what raises the water level in the bowl. For a good solid flush they all have to work together. Hope this helps and thank you for rating my reply.. Tom

The second half of my last post was what to start with if no work had been done. Check the water level in the tank. Tom also has some great starting points