\begin{table}%t3
\caption{Key water lines observable with Herschel HIFI and PACS.}\label{table:lines}
%\centerline
 {\small 
\begin{tabular}{c c c c c}
\hline \hline\noalign{\smallskip}
Transition  & Freq. & Wavelength & $E_{\rm{up}}$& Beam$^a$ \\ 
 & (GHz) & ($\mu$m) & (K) & ($''$)   \\
  \hline
\multicolumn{5}{c}{HIFI} \\
 %\hline
\multicolumn{5}{c}{Ortho-H$_2$O transition} \\  
1$_{10}$--1$_{01}$ & 556.93607  & 538.66147 &61.0 & 39  \\
2$_{12}$--1$_{01}$ & 1669.90496 & 179.65094 &114.4 & 13\\
2$_{21}$--2$_{12}$ & 1661.00802 & 180.61322 &194.1 & 13\\
3$_{12}$--2$_{21}$ & 1153.12682 & 260.16219 &249.4 & 19\\
3$_{12}$--3$_{03}$ & 1097.36505 & 273.38213 &249.4 & 21\\
3$_{21}$--3$_{12}$ & 1162.91187 & 257.97312 &305.3 & 19\\  \hline
\multicolumn{5}{c}{Para-H$_2$O transition} \\  
1$_{11}$--0$_{00}$ & 1113.34306 & 269.45872 &53.4& 21 \\
2$_{02}$--1$_{11}$ & 987.92670  & 303.66625 &100.8 &21 \\
2$_{11}$--2$_{02}$ & 752.03323  & 398.91854 &136.9 &30\\
2$_{20}$--2$_{11}$ & 1228.78902 & 244.14281 &195.9 &19\\ 
3$_{31}$--4$_{04}$ & 1893.68681 & 158.42113 &410.4 &13\\
4$_{22}$--3$_{31}$ & 916.17164  & 327.44956 &454.3 &25\\
4$_{22}$--4$_{13}$ & 1207.63890 & 248.41863 &454.3 &19\\
5$_{24}$--4$_{31}$ & 970.31524  & 309.17787 &598.8&21\\ \hline 
\multicolumn{5}{c}{PACS} \\  
\multicolumn{5}{c}{Ortho-H$_2$O transition} \\  
2$_{12}$--1$_{01}$ & 1669.90496 & 179.65094 & 114.4 & 13\\
2$_{21}$--1$_{10}$ & 2773.97691 & 108.14798 & 194.1 & 8\\
2$_{21}$--2$_{12}$ & 1661.00802 & 180.61322 & 194.1 & 13\\
3$_{03}$--2$_{12}$ & 1716.76979 & 174.74678 & 196.8 & 12\\
4$_{14}$--3$_{03}$ & 2640.47434 & 113.61595 & 323.5 & 8\\\hline
\multicolumn{5}{c}{Para-H$_2$O transition} \\ 
2$_{20}$--1$_{11}$ & 2968.74895 & 101.05267 & 195.9& 7 \\
3$_{13}$--2$_{02}$ & 2164.13230 & 138.62371 & 204.7& 10\\
4$_{04}$--3$_{13}$ & 2391.57290 & 125.44046 & 319.5& 9\\ \hline
\end{tabular}}
\medskip
$^a$ Taken from \url{http://herschel.esac.esa.int/home.shtml}
\end{table}