I searched Google only to come up with various results with different views. Is there any official or reliable source that states the impacts of keeping the WiFi router on regarding environmental impact, carbon footprint and personal health impacts?
According to this link, an average router will use 6w. Leaving it on all the time will therefore use approximately 0.14kWh per day - about the same as using a 60W laptop for 2.4 hours, or boiling a kettle once.
While it will make a tiny difference if you turn it off, there are many other things you can do that will save a lot more energy.