Bring the water and salt to a light simmer over medium to high heat.
Turn the heat down a little and slowly add in the polenta, whisking as you go to make sure there are no lumps.
Cook on a very low heat stirring for 20 – 30 minutes. If you need to add a little liquid you can add a little more water. The texture should be smooth and creamy, but thick once it is cooked.
Add in the butter, let it melt and gently stir it into the polenta.