Why water's temperature is less than air? I measured the temperature of water and found that it's less than room temperature. I think evaporation is the main reason of it. Are there any reason except evaporation for the less temperature of water?
I also noticed that the temperature difference between water and air increases when humidity decreases.
Water was on a aluminium bowl. After sometimes the water temperature increases but can't beat the air temperature
 A: It is normal for water temperature to be less than air temperature because evaporation takes heat from the water. With lower humidity in the air, evaporation is greater, increasing the temperature difference. I cannot think of any other reasons off the top of my head, and I am fairly sure there aren't any, excepting, of course, the fact that water from the tap may well be colder than room temperature, because it comes from storage where it is colder.
You will only get an equal temperature if the air is saturated with water vapour. To put that in perspective, typically air near the surface of the Earth is about 50% - 70% saturated. Deserts can be below 30%, whereas Manchester averages between 80% and 90% saturation. To obtain equal temperature, you would need to put the bowl of water into an enclosed system, which would ultimately obtain 100%  saturation if you could insulate it sufficiently to maintain constant temperature (or maybe measure it on a rainy day in Manchester, but not indoors in a heated environment).
A: This could be explained by evaporative cooling.  That would match all of the (extremely scant) information you have provided about your experimental setup and results.
If you would like a more thorough analysis of possible causes, you are going to need to write at least a couple sentences (preferably even more than that!) about your experimental setup.  What was the water contained by?  How did you measure the temperature of the water/air? How did you measure the humidity of the air?
A: A possible explanation is simply that the air and water have not equilibrated due to the high heat capacity of water. It's the same reason you can jump in a lake in the early summer and it still be cold. So if you filled up a glass from the sink and measured it 15 minutes later, it's entirely possible that it would be cooler. A more detailed description of your experiment is needed.
A: If the water is stored in a seal tight container, the water temperature will eventually equal to the surrounding ambient air.  The time it takes to get there depends on the time it takes to get the air in the container to get to the saturation point (relative humidity is at 100%) and the time it takes for the container and the water to warm up to room temperature.  More air and more water will take longer.  In a seal tight container, evaporation of water will stop at 100% humidity and there is no more heat exchanged between air and water inside the container and with time there is no heat exchanged between the container with water and the surrounding air.  No heat exchange equals to same temperature.
You can verify this very quickly by filling a water bottle half full and cover the top tightly, leave it for a day and measure the water inside the bottle.  If the room temperature has been constant, the wtare and the bottle will be at room temperature.
