When the frequency of a water wave in a ripple tank is doubled, the wavelength is indeed halved, assuming the depth of the water remains constant. In shallow water, the speed of the waves is determined solely by the water depth and gravitational acceleration. The relationship between wave speed, frequency, and wavelength is expressed as v = freq x wavelength. Therefore, if the frequency increases, the wavelength must decrease to maintain the equation's balance. This confirms that in shallow water, doubling the frequency results in halving the wavelength.