Let's say, I am washing my cloths "by hand". My steps would be:

  1. I take a basin of about 20L
  2. I pour into it some water
  3. I pour my detergent (the required amount, about a spoon) and a bit of bleach
  4. I put my cloths (for a volume of about 3L) and stir a bit.
  5. Then I let everything sit for 6 hours. After that, I rinse my cloths with fresh water.

My question is: will my cloths be cleaner, if, in step 2, I pour 15L of water rather than 5L (enough to "sink under water" all the cloths for about 2 to 3 cm) ?

Arguments in favor of 5L: the detergent and the bleach will be less diluted (but does it really mater for the bleach and for the detergent?)

Arguments in favor of 15L: the detergent will have more water to react with, to remove the stains (but does it really need 15L rather than 5L?)

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    $\begingroup$ The detergent does not need anywhere near that much water to react with. $\endgroup$ – Ivan Neretin Jul 4 '18 at 18:08
  • $\begingroup$ @IvanNeretin Are you saying not anywhere near 15L? Or 5L ? If yes, how much water does the detergent need? $\endgroup$ – Sitak Jul 4 '18 at 18:21
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    $\begingroup$ Just enough to dissolve it, if it is solid, or none at all, if it is liquid. The problem is that you'd have hard time getting all your clothes in contact with that tiny amount of liquid, hence we need to add some more, even though it would make the detergent somewhat less active. 5L is a reasonable optimum. $\endgroup$ – Ivan Neretin Jul 4 '18 at 19:11
  • $\begingroup$ How is this question opinion based? OP is looking for "answers based on facts, references, or specific expertise.", which is contrary to what the closure notice says. $\endgroup$ – Gaurang Tandon Jul 6 '18 at 3:03

The action of a detergent on the water is to lower its surface tension so the solution can wet the oily dirt in the cloth. The action of the surfactant on the oily dirt is to emulsify it by encapsulating it so it can be dispersed in the water. The amount of surfactant needed for this depends on the amount of oily dirt: more dirt requires more surfactant to emulsify it - and intense mixing helps.

Stirring a lot (not a "bit") will be much more effective in emulsifying the dirt and suspending it in the water than standing for 6 hours.

Then rinsing carries away the emulsified dirt. Some of it, anyway. More rinsing will carry away more dirt.

If you are limited by the amount of water available, a starting point would be to use one third of the water to wash, one third for a first rinse and the last third for a second rinse. Squeeze the cloth as dry as possible after wash and after rinses to remove as much of the dirty solution as possible. If you have unlimited water, use a lot of water at first, then a lot more to rinse, and rinse several times, but squeeze dry after washing and after each rinsing.


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