def efficency_hyd_poly(cappa):
    """Calculate hydraulic efficency for a given pump's typical number.

    The polynomial has been calculated applaying the curve fitting at nodes
    cappa       .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.1 1.2
    eta_hyd     .790 .820 .851 .870 .900 .911 .915 .918 .919 .920 .918
    weights     ones(cappa)
    n           5

    :param cappa (float): typical number
    :return eta_hyd (float): hydraulic efficency
    """
    coef = [0.778, -0.224, 2.011, -3.295, 2.162, -0.513]
    eta_hyd = sum([val * cappa**idx for idx, val in enumerate(coef)])

    return eta_hyd