mar/graphics/waterfall.tex

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary {arrows.meta,graphs,graphdrawing} \usegdlibrary {layered}
\tikzset{nodes={text height=.7em, text width=2.8cm, align=center,
draw=black!50, thick, font=\footnotesize, fill=white},
>={Stealth[round,sep]}, rounded corners, semithick}

\begin{document}

\begin{tikzpicture}
    \graph [layered layout, level distance=1.2cm, sibling sep=.5em, sibling distance=1.5cm, sweep crossing minimization] {
        pd [as=Problem Description] -> "Specifications" -> "Initial Design" -> "Implementation" -> "Testing";
    };
\end{tikzpicture}
\end{document}