K respectively. The effective $K_a$ of combining fourteen 25 m telescopes is $K_a\approx 1.4$ K Jy$^{-1}$. For velocity widths of 100 km s$^{-1}$, these receiving systems will reach the 1 mJy ($5\sigma$) level in roughly one to three 12 hour long integrations. The WSRT telescope will soon have the further benefit of a spectrometer capable of simultaneous observation in the synthesis mapping mode of an 80 MHz bandwidth at frequencies below 1200 MHz and 160 MHz above 1200 MHz with adequate spectral resolution for the identification of 100 km s$^{-1}$ width signals. The minimum detectable OH line luminosity as a function of redshift is plotted in Fig. \[deteclev.fig\] for a range of cosmological models and observational sensitivity.

Density of megamasers per solid angle
-------------------------------------

Estimates for the number of detectable megamasers in a blind survey of a large area of sky can be straightforwardly obtained by computing the comoving volume at redshift $z$ contained in the solid angle $d\Omega$ and depth $dz$ (Wieringa et al 1992), $$\begin{aligned}
dV &=& 4\left(\frac{c}{H_o}\right)^3
\frac{[\Omega_oz+(\Omega_o-2)(\sqrt{1+\Omega_oz}-1)]^2}
     {\Omega_o^4(1+z)^3\sqrt{1+\Omega_oz}}  dz\,d\Omega, \nonumber\end{aligned}$$ and then filling the volume with OH emitters according to the density prescribed by Fig. \[OHLumfnct.fig\]. A count of the number of objects whose observed flux 