Left alignment of text in table

Question

how do I left align this table? I do not want to justify it.

    \centering
    \caption{Characteristics and classification of hydrological model}
    \begin{tabular}{ p{4.9cm} p{4.9cm} p{4.9cm} }
     \hline
     Empirical model & Conceptual model & Physically based model \\
     \hline
     Data based or metric or black box model & 
     Parametric or grey box model &
     Mechanistic or white box model \\
     \hline
     Involve mathematical equations, Derive value from available time series &
     Based on modeling of reservoirs, Include semi empirical equations with a physical basis &
     Based on spatial distribution, Evaluation of parameters describing physical characteristics \\
     \hline
     Little consideration of features and processes of system &
     Parameters are derived from field data and calibration &
     Require data about initial state of model and morphology of catchment \\
     \hline
     High predictive power, low explanatory depth &
     Simple and can be easily implemented in computer code &
     Complex model. Require human expertise and computation capability \\
     \hline
     ANN, Unit hydrograph &
     HBV model, TOPMODEL &
     SHE or MIKESHE model, SWAT \\
     \hline
     \end{tabular}
    \source{Gayathri K Devii et al. (2015) \cite{CITE26}}
    \label{tab:table2}
\end{table}

Answer 1

I suggest you (a) switch from a tabular to a tabularx environment and set the width of the tabularx environment to \textwidth, (b) use \RaggedRight in all 3 columns, and (c) use fewer but well-spaced horizontal rules.

\documentclass{article} % or some other suitable document class
\providecommand{\source}[1]{{\footnotesize\raggedright Source: #1\par}} % ??
\usepackage{tabularx,ragged2e,booktabs}
\newcolumntype{L}{>{\RaggedRight}X}

\begin{document}
\begin{table}
\caption{Characteristics and classification of hydrological model\strut}
\label{tab:table2}
\begin{tabularx}{\textwidth}{ @{} LLL @{} }
     \toprule
     Empirical model & Conceptual model & Physically based model \\
     \midrule
     Data based or metric or black box model & 
     Parametric or grey box model &
     Mechanistic or white box model \\
     \addlinespace
     Involve mathematical equations, derive value from available time series &
     Based on modeling of reservoirs, include semi empirical equations with a physical basis &
     Based on spatial distribution, evaluation of parameters describing physical characteristics \\
     \addlinespace
     Little consideration of features and processes of system &
     Parameters are derived from field data and calibration &
     Require data about initial state of model and morphology of catchment \\
     \addlinespace
     High predictive power, low explanatory depth &
     Simple and can be easily implemented in computer code &
     Complex model. Require human expertise and computation capability\\
     \addlinespace
     ANN, Unit hydrograph &
     HBV model, TOPMODEL &
     SHE or MIKESHE model, SWAT \\
     \bottomrule
\end{tabularx}

\smallskip
\source{Gayathri K. Devii et~al.\ (2015) \cite{CITE26}}

\end{table}
\end{document}