Sink/Dishwasher water into rainwater drain?

We're planning on moving our waste water exit pipe for sink/dishwaser/washing machine from one side of the kitchen to the other and though we could use a outside drain on the new side rather than the old drain.

However, I'm told that waste water cannot go into the same drain as this is used for rainwater from the house gutters and that we'd have to route the pipe back to the original drain.

Now while I don't doubt this is the case I really don't see why. Is there two completely separate drain systems coming from modern houses (built 1997), and these never mix or do the two drains meet half way down the garden?

You should not (prohibited by building regulations and local authority bylaws) combine foul water and surface water together. Remember afterall that surface water run-off will eventually end up in the public water supply! Dishwashing water will be full of fat and grease in solution plus the detergent chemicals, this is not good stuff to be going into a surface water drain which is essentially untreated.

Good morning Carpenter! Does that mean that there are two seperate sewers leading away from houses?

Do not do this. Somebody did this in my row of houses, I have the end of line manholes in my garden, both foul and rainwater. The sewer pipe had broken anyway outside on the road causing a backflow of surface water into my garden. The Council were so annoyed because the water was clearly polluted with shampoos, detergents etc, where somebody had done which you are suggesting. It does cause problems with scum and grease build-up, causing trouble in the future. It's also illegal.

Simeon said:

Good morning Carpenter! Does that mean that there are two seperate sewers leading away from houses?

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In the past (especially in smaller towns and outside of the main population centres) it was not uncommon to have a "combined" sewer system, whereby foul and surface water drains were run separately out to a combined public sewer. In most cases these combined systems have been replaced with a two pipe (foul and surface water ) systems.

Interesting! Yup, I am from a (very) small town and am no spring chicken. The idea of two sewers running down the main street seems superfluous but I guess it makes good sense. Do these pipes then meet - what I mean to say is - are they treated as seperate items in the treatment centre or are they combined before treating?

Surface water drains are generally piped (untreated, except perhaps to remove oil or fuel residues) to the nearest river, whereas foul water sewers are piped to a treatment plant, the resulting treated effluent is then discharged to a river (the remaining sludge is spread on agricultural land). This interesting link will explain all you need to know! http://www.iol.ie/~cea/sewage.htm

Thanks Carpenter, all makes sense to me, much appreciated.

DaveD