I don’t use shampoo , just soap and shaving foam.
Planning to fit a diverter on the drain pipe outside to collect the water for plants.
Will the flowers be ok ?
Shall be saving rainwater for anything edible.

I ‘think’ it should be fine. Flowers have their own filtering system so as long as your soap is biodegradable (which I think most are) and the dilution rate is fairly high then there shouldn’t be any problems. Only drawback might be the soap marking / leaving a residue on the flowers, so you may want to water around the roots. On the flip side soap is great for getting rid of aphids so watering over the leaves will keep the bugs away. Spraying plants with a water / washing up liquid mix has been used as a way to get rid of greenfly for years, and I have never heard of it being a problem to the plants. Even on vegetables.

The only thing I’m not sure about is the shaving foam (not sure what it contains) but the dilution should be good enough to sort it out. The rain that falls will contain as many ‘bad’ petrochemicals as any soap / shaving cream solution would.*

*probably 😉

I’d love to build my own house with a fresh and a ‘grey’ water system – was thinking of a 2000+L drum buried in the garden, collecting rainwater and shower water to be used for watering duties and flushing the loo – it pains me that we use drinking water to flush our toilets!!

It’s on the bucket list I guess!

DrP