A method to generate a broadband water window continuum high-order harmonic generation spectra is proposed using a few-cycle two-color driving pulse synthesized by 2000 nm mid-infrared laser driving field and its much weaker 1000 nm second harmonic modulation field. In the scheme, the ionization step can be modulated by the weaker second harmonic, which not only broadens the bandwidth but also enhances the yields of the continuum harmonics. By solving time-dependent Schr?dinger equation based on one-dimensional helium atom model, it is found that a broadband continuum harmonic spectrum with bandwidth of 190 eV is observed and the yield of the continuum harmonics is increased by two orders compared with one-color 2000 nm driving field alone. Furthermore, adjusting the carrier envelop phase between the two-color field can enhance the contribution of one ionization trajectories and simultaneously suppress the other one, from which an isolated 70 as pulse can be obtained.