def m2qh2o(m_H):
    """Convert helocentric magnitude, m_H, to Q(H2O).

    Based on an empirical correlation between heliocentric magnitude
    and Q(H2O) by Jorda et al. (2008, ACM, 8046).  Scatter about the
    trend: 1-sigma = 1.6, 2-sigma = 2.4, 3-sigma = 3.7.

    Parameters
    ----------
    m_H : float
      Comet's heliocentric magnitude = m_V - 5 * log10(Delta).

    Returns
    -------
    Q : float
      Q(H2O) at 1 AU.  [molecules/s]

    """
    return 10**(30.675 - 0.2453 * m_H)