Wikipedia:Reference desk/Archives/Science/2020 January 9

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 9

Minimising water wastage

I may have asked a related question some years ago, but in any case let me rephrase it.

When I turn my shower on, there's a short lag while the hot water reaches me. If my aim is to minimise water wastage, is it best to have the volume turned to high, or low, or some optimal point in between, or does it make zero difference what I do? -- Jack of Oz ^{[pleasantries]} 19:07, 9 January 2020 (UTC)

I'm sure the volume makes a negligible difference. I start at maximum heat and adjust as it goes to reduce water waste. Your best option would probably be to install a different kind of water heater that doesn't have lag due to pipes. One behind the showerhead rather than in the cellar or what have you. These exist, I don't remember the name for them. But: one is unlikely to affect much of anything by their shower duration. One's cumulative water use depends much more heavily on the products and foods they consume, and the companies they patronize. The shift of the burden of environmental damage from corporations to individuals is a bamboozle. Temerarius (talk) 19:50, 9 January 2020 (UTC)

As a measure to reduce an individual's total cumulative water use Temarius is doubtless correct. But JackofOz did not raise the issue of environmental damage, and may (as I do) inhabit a domestic property whose water use is metered and charged by volume, in which case measures to reduce the water usage of that property can impact significantly on the wallet of the person who pays its water bill.

My domestic supplier (Southern Water, in the UK) includes in its bills a table of daily water use for "typical" households of from one to six persons, viz: 6 - 548 litres, 5 - 493, 4 - 438, 3 - 370, 2 - 274, 1 - 178. My most recent bill, covering April–September inclusive 2019, shows my (single-person household) usage as 22 litres/day, around 12% of "typical", so clearly there is considerable scope for reducing one's domestic water usage (and resultant bill).

Regarding JackofOz's hot-water lag period problem, one possible measure might be to hold a bucket under the shower head until it begins to flow warm, and re-use the collected water for some other purpose, such as watering garden plants or filling the WC cistern. {The poster formerly known as 87.81.230.195} 90.204.182.54 (talk) 20:53, 9 January 2020 (UTC)

If taking a bath, the too cold water that comes out first can be mixed with the too hot water that comes out later to produce just right water, with no waste. However, the cold will tend to stay at the bottom and hot at the top, so mixing will take some effort. NonmalignedNations (talk) 22:19, 9 January 2020 (UTC)

It's about 20 seconds typically at full blast, that's 3 or 4 litres. It makes no difference volume-wise whether you open the tap fully or not, you need to expel all that cold water between the hot water source and the shower head. I'm on rainwater, so towards the end of the summer I have to get used to starting my showers icy cold! Greglocock (talk) 22:46, 9 January 2020 (UTC)

It might make a difference volume-wise depending on the heat capacity of the pipe (thermal mass, insulation in cold spaces, etc) because it's not just "hot pushes cold" (volume is the pipe volume), but the water cools down as it heats the pipe along the way until the pipe is up to equilibrium temperature. @Temerarius: seems to be thinking of a tankless water heater. DMacks (talk) 04:06, 10 January 2020 (UTC)

I am familiar with the predicament described by JackofOz. Some of the hot-water taps in my house are a long way from the water heater (gas-fired.) During the protracted period of drought and water restrictions in 2003 everyone in my house got into the habit of putting an empty milk carton under the hot tap and filling it until the hot water arrives. Later, the milk carton is emptied into a watering can for use on the garden. It proved to be such a good idea that we keep doing it, even though the drought and water restrictions ended after 4 or 5 years. Dolphin (t) 04:55, 10 January 2020 (UTC)

Collect the initial cold water in a bucket and use it to flush the lavatory.--Shantavira|^{feed me} 09:43, 10 January 2020 (UTC)

In luxury yachts there is the option for instant hot water as the hot water pipe circulates continuously to the boiler, called hot water circulation. That would solve your problem, but it is probably not a cost-saver Rmvandijk (talk) 10:02, 10 January 2020 (UTC)

• If the shower is used in a morning shit-shower-shave routine, the hot water lag will waste less water if the toilet can be flushed from the hot water supply. (A special plumbing arrangement would be needed, possibly as a third option on a Dual flush toilet).

• Often hot water is supplied from a tank where it is heated to a higher temperature than used for showering. The water loss during the delay in the pipe before tolerably warm water flows in the shower can be minimised by starting with 100% hot / 0% cold mixer tap setting. To control this manually risks scalding but Thermostatic mixing valves can be fitted to achieve it.

• The "Navy shower" method conserves water and energy by turning off the flow of water in the middle portion of the shower while lathering.

• You may consider whether various ideas for Water recycling showers appeal.

• In a space station where water is at such a premium that a Life support system may reclaim potable water from urine, Skylab had a shower for use without gravity: the user was surrounded by a curtain, water was sprayed in and then removed by a vacuum cleaner. Quora has addressed questions such as How do astronauts wash themselves in space? and How do astronauts bathe in space? How do they dispose of their waste?. DroneB (talk) 13:02, 10 January 2020 (UTC)

If you are able to and it's not already done, consider insulating your pipes. According to [1], the water will still only stay hot for about 30 minutes or so, but may still be useful especially if there are multiple people using your shower, or you take a while to lather etc with the shower off. And if you have access to the pipes and sufficient mobility, it's a relatively easy and low cost DIY task. Nil Einne (talk) 04:55, 11 January 2020 (UTC)

The insulation will have a secondary benefit. That is, it will reduce heat loss from the pipes after they've reached maximum temperature. With a long path of uninsulated pipes, you might notice that the maximum water temperature at the tap is considerably lower in winter, due to this heat loss. NonmalignedNations (talk) 14:52, 11 January 2020 (UTC)