I assume that you refer to the practical aspects of sample collection and system maintenance/treatment etc, and not the laboratory testing aspect that is a specialist undertaking.

Many companies offer consultancy services to supplement their chemical and microbiological laboratory testing services and will work with you to set up a protocol for your own use that is both safe and efficient, and importantly is comprehensive with regard to your water system(s). An in-house approach may be fine, but there are many pitfalls and this may be money well spent to avoid trouble in the future.

As for a practical hint, make sure that water collected for laboratory examination is collected properly, without extraneous contamination, into a suitably labelled sterile container and that it is transported to the lab without delay. This will avoid many wasted samples that are unsuitable for culture or overgrown with contaminants.

I can suggest one London-based company to advise if you want to PM me, but I will make it clear that I have a link with that company and there are no doubt many more that you could choose.

Ian