Water hammer is caused by moving water being abruptly stopped creating a pressure wave.
Causes: quick-closing valves, high water pressure above 500 kPa, long pipe runs, loose pipes, failed arrestors.
Dangers: damaged pipe joints, burst flexible hoses, appliance damage, loosened pipe clips.
Fixes: install water hammer arrestors $30-$60 each, install pressure limiting valve $300-$600, secure loose pipes $150-$400, replace quick-closing taps.
DIY temporary fix: recharge air chambers by draining all pipes and refilling..