When a tuning fork was brought close to the pipe filled with water

When a tuning fork brought close to the pipe filled with water increased frequency is produced.
As we know that the speed of sound is different in different media. The fork is vibrated in the air and, when brought close to the mouth of the pipe, filled with water. Energy transfers to the water. 

But the sound speed in water is more than that in air. As we know:
$\mathrm{Speed}=\mathrm{wavelength}\times \mathrm{frequency}$. 

The frequency will also be increased as the speed increases.