We only started home dialysis 11 years ago and have always done HDF on Fresenius 5008S.
Before starting, I spoke to a German Fresenius development engineer who also dialyses at home on HDF; he saw no need to be concerned.
No additional precautions were deemed necessary.
Hardness sampled by the patient regularly, shedloads of carbon filtration and 6 monthly RO water ubio and chem samples.
Initially four of our most dependable patients took HDF fluid samples monthly for us. We only had about 4 results >1 cfu, all were under 5. Each of those >1 the patient had been unsure that they had done the sampling properly.
As a result, and as there are 2 levels of ultrafiltration, we don't do any HDF or dialysis fluid samples. We also stopped doing these samples in our units too.
Only had a brief period of experience with home HDF as patient received transplant. No additional issues noted in that time. We had a hardness level of 7.56 degrees Clark and ran a Purite/Suez RO1500+ UF without water softener. Typically 800ml/hour dialysate flow used here. We maintained our usual home microbiology sample frequency of every 3 months while it in use of the RO.