The Chinese Tea is usually really strong. So, the chinese people will keep adding more water without changing the tea. To indicate that they need more water, they will take off the lid. The tea house, restaurant, bar staff will then come to pour some more water.
This practice seems to be based on an old chinese legend...
Once upon a time, in a small tea house in the suburbs of BeiJing, an old traveller was drinking tea and reading some poems from Lu Xun. Then, the waitress arrived and removed the lid to see if the old man needed some more water...
The old man jumped on his feet and angrily said to the waitress that a really rare bird was in the tea pot and that she let it go away! So, the unfortunate waitress had to pay for the bird...
Since then, the tea house staff members will always wait for the customer to remove the lid by himself.