No, not even. As i think i've stated in this thread already, theres evidence to suggest that levels of up to 400ppm can be withstood with no ill effects, and 20ppm has no real significance to anything. Some peoples tap water can have levels higher than that.
I think the highest concentration from the tap i've heard of is 80ppm, so it would be reasonable to suggest that 100ppm would be a good maximum to aim for in the quest for optimum fish health, as it's well within the researched safe levels and is not above the level of most tap waters.
That said, the best recommendation in my opinion, is not to specify a specific value but to suggest that aquarists keep nitrate levels as close as possible to the level from the tap. This is a good indication that your aquarium maintenance schedule is sufficient.