Even though my property is only 20 miles from the centre of the Sydney (largest city in Australia) there is no mains sewerage system available. All waste water from the house (kitchen, laundry, toilets... the lot) goes into an "Aerated Water Treatment System" and is sprayed out onto the lawn. What comes out is perfectly clear and is slightly chlorinated. I am assured it is not a health hazard (though one is told not to use it on vegetable gardens) The "irrigation sytem" is simply a poly pipe about 40 metres long with spray jets every couple of metres. The pipe just lies on the lawn so it can be moved about if any area becomes too wet (but this is never a problem). My question is what can I do about the weeds that seem to grow so prolifically along side the pipe. Why do the nutrients seem to do more for the weeds than the grass? Apart from moving the pipe a couple of metres side to side for mowing purposes, I do not move it around too much for fear of extending the weeds even further or would I do better to move it around more and subject a greater area to a lesser dose?