Although it may be negligible, it is always a cost
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Fair point but it would be in pence per square meter.
If you are charged for water and electric plus fuel then they would be bigger costs.
If you use a colloid cleaner like bio clean or M power then you are looking at a dilution of 120 to 1 or 8.3 mils per litre. 5 lts cost £45 concentrate. Guessing now but probably .01 of a pence per square metre.
The Alltec detergent one probably works out at .05 pence per sqmt. So it is really negligible.
I guess a better question would be how much profit can you make per 5 lts of concentrate. That depends on what you charge.
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MPower is harmful for oriental rugs!