When cooking tomato sauce for a long time, should you add water? I know tomato sauce should be cooked for a long time to develop flavor. To prevent it burning you have to stir constantly, though I find it burns on the stove (and the oven) too much without adding water.

I wonder however if adding water can stop the sauce from developing flavor since boiling food cannot reach 300+ temperatures required for flavor to develop. Lately I found putting a lid on the skillet reduces evaporation and thus chance for burning, though I think it may defeat the purpose.

When cooking tomato sauce, does adding water to prevent sauce from burning stop the flavor development?
Tomatoes are mostly water anyway. They're not going to get above boiling point whether or not you add water (or at least not by more than a very few degrees even with salt added - less than the effect of altitude). 

On the other hand the browned bits from the bottom of the pan (often called fond in the US though I've never heard this in the UK and the usage in France is a bit different) do give a nice flavour to the sauce so long as they don't catch. 

If you do add water, you'll need to simmer it down anyway, making that the stirring step still happens, just later. But adding some water fairly early can give you some flexibility. A good time to do this is when it's starting to need constant stirring but you need to get on with the rest of the meal. A low heat and a heavy pan help too.