KJ, Wellington.

To keep a shower clean without harsh (and expensive) chemicals, get the last person to use the shower to hose down the walls (if you have a handheld shower head), then wipe the walls and floor with a micro fibre cleaning cloth. These cloths are indispensable for cleaning without much more than soap, baking soda, or vinegar for tough cleaning. Hosing and wiping down the shower prevents the build-up of soapy scum.