Earth Notes: On the Cost of Washing

What is the water, energy cost of adequate hygiene? Cleanliness need not be next to impossible...

TL;DR - even if water itself might not be a problem, heating to get clean it uses a lot of energy, so saving water saves money and carbon!

On this site I'm primarily interested in energy costs and the resulting carbon emissions.

Water is not usually in short supply in the UK (including London) though the drought of 1976 is still firmly in my mind, and it's a resource worth conserving and may become more scarce with climate change and energy shortage. For example, London may have to consider firing up some energy-intensive desalination plant soon.

I was originally provoked to write this note by an advert in the Times 2009/03/07 for the ecocamel water-saving showerhead (which injects air into the water stream), claiming to save up to £250 per year per household in water and energy bills (40%/55,000l less water showering per year). The ecocamel showerhead cost about £25 in 2009; £30 upwards in 2017.



Very much to its credit the ad explains some of its assumptions and calculations in reaching the estimated savings. Now our gas tariff (with a standing charge) comes in at about half the cost per kWh quoted in the ad, and even if our water was metered our per-m^3 charge would be lower than that indicated in the ad, and only one of us in our household of four currently takes a shower, thus we couldn't possibly currently achieve the savings suggested, though only one tenth would be enough to pay for itself financially in a year.

Some largely spurious though interesting 'facts' (unverified by me, source not cited) quoted in the ad are:

Assumptions quoted in their savings calculation are (vs our situation):

Cost of Showering and Bathing

For my bath as of 2009/03/08 ~4/week assumed water usage each time ~100l (~16p as metered/billed by Thames Water), energy <4kWh <12p gas heated).

The two children have shallower, cooler baths, about 4/week also.

One adult takes a similar number of showers per week.

By reducing my (already shallower, cooler) baths from daily to every other day we saved ~2kWh/day gas in 2009 compared to 2008, bringing the total cooking/DHW consumption down from ~8kWh/d to ~6kWh/d. In 2009 I will try to replace most of my baths with showers to aim to save up to another 2kWh/day (~730kWh or 139kgCO2 per year).

As of 2012/12 a new Flowpoint showerhead and a 4-minute shower timer free from Thames Water may get my occasional shower down to <30l and <2kWh. A quick measurement 2013/01/06 with mains water at ~10°C indicates a consumption of about 0.032m^2 gas or 0.34kWh/min while showering (ie a little over 20kW given a nominal boiler output of ~24kW), ie for a 4 minute shower, and allowing for warm-up time, ~1.4--1.6kWh.

Cost of Washing Dishes

In the dishwasher as of 2009/03/08: washing tablet <10p, electricity >10p (0.86kWh for normal 'quickwash' programme with inlet temperature between 10°C and 20°C), water consumption 18l specified in manual (though not clear if this includes prewash/rinse) thus <10p as metered by Thames Water.

We do some washing by hand in the sink, but relatively little.

Maximise energy and water efficiency by running your dishwasher full and if necessary buy more of whatever cutlery/dishes you run out of fastest so that their lack no longer forces you to run a load prematurely!

Cost of Washing Clothes

See how we've reduced the cost and CO2 emissions of washing with our new machine. As of February 2010 we do maybe 25% or a little less of the washing on cold (the mains water temperature is low enough right now to have even low-temperature detergents such as small & mighty struggle with significantly-soiled clothes), but the clear majority on 30°C, some tough stuff on 40°C, and once a week a towels and machine 'maintenance' wash on 60°C. Almost all the non-cold washes are done on delay to finish at breakfast time which is convenient and causes less CO2 emissions from the grid than drawing the power later in the day. May annoy very light sleepers though! Compared to our previous machine and regime we may be saving half a unit (and ~0.25kgCO2 emissions) every day on average.

In our (old) washing machine as of 2009/03/08: washing tablet <10p, electricity >10p (cold fill for a 40°C wash with 0.74kWh and inlet temperature between 10°C and 20°C), water consumption 63l specified in manual thus ~10p as metered by Thames Water.

For maximum energy and water efficiency make sure that you run the machine full and if necessary buy more of whatever you run out of fastest so that its lack no longer forces you to run a load prematurely!

With our new washing machine, ~10% more energy efficient (and even more water efficient) anyway, we have an alternative which is to use a cold cycle saving 80%--90% energy but using a more advanced and expensive detergent to compensate, leaving us at about the same per-wash cost financially.

Given an assumption therefore of a 2009 cost of ~30p for a 5kg load (6p/kg), and given some figures suggested by Zanussi for clothing weights (see below), we get a cost of maybe 1p for briefs/underpants, 3p for a business shirt, 3p for pyjamas, 3p for a sheet or duvet/quilt cover, and maybe 7p for a bathrobe / dressing gown / housecoat.

Some of Zanussi's indicative laundry weights:

ItemApprox Weight
bathrobe 1200g
quilt cover 700g
man's work shirt 600g
sheet 500g
man's pyjamas 500g
tablecloth 250g
pillowcase 200g
man's shirt 200g
night dress 200g
tea cloth 100g
blouse 100g
ladies' briefs 100g
men's underpants 100g

Laundry Detergents for Cold(er) Washes

Something like 90% of the energy that goes into a typical domestic washing-machine cycle is expended in heating the water; being able to wash at a lower temperature is a potential energy saver.

There have been programmes in the UK/EU such as "turn to 30" to encourage washing at 30°C rather than 40°C or hotter, and those are valuable, but being able to wash in cold water as is common in the US and Canada would be vastly better still.

As of August 2009 the lowest-temperature widely-available laundry detergent is the Ariel Excel gel (and Fairy gel) at 15°C from Proctor and Gamble. The cold water inlet in London at least is only at/above 15°C for about half the year, thus apparently precluding cold washes entirely in winter. However, P&G makes "Tide Coldwater (HE)" in the US, rated down to 4°C, which might work well here, but is not willing to sell it in the UK. Doing most or all UK domestic washes (consuming nearly 5TWh electricity annually circa 2007 out of ~400TWh UK total, or ~0.5kWh/d per household corresponding to maybe less than one wash per day, see IBNW23 at in cold water could save a noticable fraction of our entire energy consumption. I was sufficiently annoyed by this 'market failure' that I forwarded my response to Ed MiliBand at DECC. On re-analysis of the numbers, domestic laundry probably only accounts for 1% of domestic electricity consumption, but that's still significant and there for the taking if P&G (and presumably Unilever) would sell existing formulations in the UK.

In October 2009 we bought some (Unilever) Persil "small&mighty" at an offer price of ~10p/wash and clearly labelled as good down to 15°C (though Unilever customer services said that all their pure liquid detergents, eg not capsules, are tested down to 10°C), and it works well even below 10°C and indeed we prefer it to the Ariel.

Other Washing Costs

We have a big old (9l?) WC albeit with a water-saving device, and though we follow a "if it's yellow, let it mellow" policy since flushing a few hundred millilitres of dilute (sterile) urine at most with several litres of potable tap-water is horribly wasteful, its flush is not always fully effective, so I imagine its consumption remains a significant fraction of our total.

We don't have a car to wash, so that's one significant avoided cost!

As to the washing costs calculated above, ideally I should compute/include the CO2e emissions of the water and detergent with the electricity/gas to get a fuller measure of the environmental rather than financial costs.