Extreme ultraviolet (EUV) emission in the 11-15 nm wavelength range from a thin liquid water jet target under illumination with a high repetition rate, high average power laser (Nd-YLF) has been studied. To find the optimum conversion efficiency of laser light into EUV radiation, different laser parameters were applied. The laser intensity was varied between 10(11) and 10(15) W/cm(2), and pulse duration in the range from 30 ps to 3 ns. A maximum conversion efficiency of 0.12% in 2.2% bandwidth and 4 pi steradian at 13 nm was achieved at a repetion rate of 250 kHz, and a strong dependence of the conversion efficiency on both laser intensity and pulse duration was found.