how do water companies calculate the waste water part of the bill?

[Roskva]

The water that comes in is metered. How do they measure what goes out? On our bill it amounts to more than half the total cost for 5 cubic metres less in volume. But how do they know the difference is 5 cubic metres?

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With mine they just take a percentage of the water coming in and charge that for waste going out. I don't know the percentage. I think it is something like 90%

I remember ringing up as a student to ask them this, but I can't remember the answer. I also remember asking them if they would lower the cost if I promised to mostly wee at Uni - so I think that wine may have been drunk.

The water has to go somewhere, so I think they just assume an amount based on what you take in.

Just checked my bill and it is based on 90% of the water coming in

lol, Twentypence.

So it is fairly arbitrary, then

I suppose it's going to work out about right isn't it.

You can normally get a discount if you can prove rain water isn't being added to you waste water (through water butts, recycling etc)

What if you water the garden/wash the car/etc a lot?

With rain water or metered water?

One doesn't count & the other would cost more

It's a sort of hypothetical question, as we have no garden to speak of, but I do water my pots with metered water, so that is water that is not going into the domestic waste. It might be a question to get my dad going, as he has a huge garden watered with metered water, so theoretically when his water consumption is highest (in summer), the level of his waste water is still approx the same as the rest of the year, so technically he's probably paying for more waste water than he is actually wasting. I think that makes sense - my brain is particularly mushed today.

If any rain water goes into the sewers then I think you can't get the discount - so any drive or patio with a run-off would prevent the discount

It's a sop rather than a benefit