Chlorination of water services is usually the last water related operation carried out before a plumbing job is handed over. In essence, chlorinated water is flushed through the pipework which is then left to stand for a set period of time. This pipework is then flushed out. After flushing, the samples are taken for laboratory tests. If the job has not been done properly, the samples can fail.
If we have a failure, we do the job again FOC. In twenty years of this type of work we have only had one failure and we did the job again and it failed again. Third time lucky, with a high chlorine dose rate, the samples passed. I found out eventually that the pipework, (63mm MDPE) had been stored outside, with open ends, for twelve months. In that time the local rat population would have used the pipework as a lavatory. The customer was not a bit grateful for all our efforts at finding the problem!
The moral of this story is always store pipework under cover with the ends sealed. If you can’t do this, tell your Chlorinators who would probably dramatically increase the chlorine dose rate.