  In the minimal Standard Model (MSM) with three generations of quarks and
leptons, neutrinos can have tiny charges consistent with electromagnetic gauge
invariance. There are three types of non-standard electric charge, given by
$Q_{st} + \epsilon(L_i - L_j)$, where $i, j = e, \mu, \tau$ $(i \neq j)$,
$Q_{st}$ is standard electric charge, $L_i$ is a family-lepton--number, and
$\epsilon$ is an arbitrary parameter which is put equal to zero in the usual
incarnation of the MSM. These three non-standard electric charges are of
considerable theoretical interest because they are compatible with the MSM
Lagrangian and $SU(3)_c \otimes SU(2)_L \otimes U(1)_Y$ gauge anomaly
cancellation. The two most conspicuous implications of such non-standard
electric charges are the presence of two generations of massless charged
neutrinos and a breakdown in electromagnetic universality for $e$, $\mu$ and
$\tau$. We use results from (i) charge conservation in $\beta$-decay, (ii)
physical consequences of charged atoms in various contexts, (iii) the anomalous
magnetic moments of charged leptons, (iv) neutrino-electron scattering, (v)
energy loss in red giant and white dwarf stars, and (vi) limits on a
cosmologically induced thermal photon mass, to place bounds on $\epsilon$.
While the constraints derived for $\epsilon$ 10^{-21}$), the $L_{\mu}-L_{\tau}$
case allows $\epsilon$ to be as large as $10^{-14}$.
