I am trying to scale my mindmap tikzpicture down in beamer, but I am unable to reduce the size of the circle in the middle.
\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{mindmap}
\tikzset{level 1 concept/.append style={font=\sf, sibling angle=72,level distance = 25mm}}
\tikzset{level 2 concept/.append style={font=\sf, sibling angle=45,level distance = 15mm}}
\tikzset{level 3 concept/.append style={font=\sf, sibling angle=45,level distance = 15mm}}
\tikzset{every node/.append style={scale=0.6}}
\begin{document}
\begin{frame}
\begin{tikzpicture}[mindmap, grow cyclic, every node/.style=concept, concept color=blue!40, align=flush center]
\node{Water}
child { node {River pollution}}
child { node {Water supply}}
child { node {Water reuse}}
child { node {Water conservation / demand}}
child { node {Changing thoughts around water use}}
;
\end{tikzpicture}
\end{frame}
\end{document}