I’ve spent the last 15 years or so exploring, analysing and investigating water efficiency.  But for the last few years, there is one day a year when I ignore my own professional advice and do something unspeakable in my back garden: I power wash my patio…

Up until now I’ve been ashamed to talk about this act, fearful of the reprimands and weird looks from colleagues and clients.  But finally I decided to face my demons and analyse this annual orgy of water use.

So with trepidation I took a meter read before I started the cleaning, another one when the main clean was complete, and one after I had finally put the little yellow machine away for another year.

So, some vital statistics!

My back garden is mostly patio and borders.  I estimate the patio area to be about 260 square meters.

The patio is made of natural stone slabs which collect gunk from rainfall, mainly over the winter – hence the need for annual clean.  You can see the effect of the cleaning in the photo below, with one slab before and after being washed.

I have a Kärcher K2 Compact pressure washer.  It claims to deliver a maximum of 360 litres per hour (i.e. 6 litres per minute).

I actually used around 400 litres on the patio, based on the meter reads.  The different between the start and end meter reads was about 450 litres but there was some other water use going on at the same time (mainly a washing machine cycle), therefore an estimate of 400 litres.

About 250 litres of this was used in the main clean, using the circular patio cleaner attachment you can see in the picture. The remaining 150 litres was used with the lance attachment, spot cleaning bits I’d missed and removing some dark patches on the wall you can see at the rear of the garden.

I estimate the patio cleaner attachment is about 50% more water efficient than just using the normal lance attachment, mainly because when I first got it, it roughly halved the time it took to do the job. Maybe that’s why this product is Waterwise recommended.

As for my water inefficient behaviour, I make the following points:

  • It’s only once a year (I resist calls for more frequent washes…)
  • Four hundred litres over 260 square meters works out at just over 1.5 l/m2.  You might use less with a scrubbing brush, but life is too short!
  • We use very little water in our garden for the rest of the year, as it’s mostly shrubs and trees in the borders.  We just water the pots if it’s dry.
  • It’s less than a day’s use for our family – less than one percent of our total annual use.
  • That patio wasn’t cheap and it looks great when it’s clean.
  • I’m on a water meter, so I pay for what I use.
  • This job costs me about £1.50p in water and sewerage charges. Well worth it.

Now who else has a water inefficiency secret they want to share!