I've been following this thread for some time and wanted to offer a few comments. My post is somewhat long but hopefully not too boring. It might even be useful to some following this thread.
Low, ppm levels of phosphate can precipitate with calcium. pH and temperature influence this solubility. Calcium phosphate solubility is reduced with increasing temperature and pH. Some detergents will include additives to address water hardness issuues. Modern detergents are something of technical marvels in and of themselves and along with "soap" and enzymes there will be a whole laundry list (pardon the pun) of other chemicals that would be be applied to the vinyl surface if used for LP cleaning. I do think Jan's idea is worth experimentation -maybe with some heavily soiled, flea market LPs that are beyond any other means of saving. I would probably do a thorough rinse with good quality water before any steaming.
On the topic of best process for producing high quality water...just an observation that for distillation, the number of stages, and for RO, the number of "passes" (times water is pushed through a membrane element) will influence the outcome. Single pass RO may reduce calcium and other dissolved minerals by 90% or so. Multi-pass RO can lead to a significantly better quality water than single pass. RO coupled with demineralization (charged resins that adsorb dissolved minerals) followed by electrically-based polishing steps will yield some of the highest quality water possible. All this to simply point out that citing RO water does not guarantee the same quality product from source to source since there is much potential variability in the process as practiced one location to another (not to mention post-production handling as in quality of transfer lines and storage vessels). Same things apply to distilled water. I'm not coming down on one side or the other of the RO vs distilled water discussion. I believe there are multiple paths to the same endpoint (clean vinyl). Find the best quality water you can afford and easily obtain. During the search, if possible, investigate the details of the process used to produce it. Personally, for steaming, I just use distilled water bought at the grocery store with vacuum as a final/drying step.
On the topic of cleaning LPs with bacteria and how water quality might affect this...
Many common, garden variety bacteria utilize organics [generically Cx(H2O)y]to generate energy and build new cell mass. They do need trace amounts of a range of minerals. The acronymn CHOPKiNS is sometimes used as a mnemonic for nutrients required by microbes: Carbon, Hydrogen, Oxygen, Phophorus, Potassium, inluding Nitrogen and Sulfur. Other elements like Mn are also needed though in even lower amounts. Typically H & O are in abundance from water. Carbon is what usually limits growth since they need more of this than N, P, K or S. If you supply only minerals to a population of microbes but limit carbon source to a specific compound, it is possible to determine whether that compound is biodegradable based on whether the organisms grow or not.
Regarding Charlie's musing about water quality influencing efficacy of bio-mediated cleaning...if water quality is such that the bugs have no other source of organic material than the crud in an LP groove...that can well become the primary focus of their attentions if it is organic and biodegradable. As a closing illustration, various industries require extremely high quality water (chip mftrs, for instance). Water treatment systems at these facilities represent major capital investment and are capable of producing extremely high quality water, chemically and biologically. The manufacturing equipment itself can still experience problems due to biological activity, however. In such systems - as nutrient poor as they are designed to be - microbes can extract sufficent material for growth from various plastics and other elastomeric compounds used in construction along with trace organic contaminants present on surfaces. Use of microbes to clean an LP groove is not far fetched at all given adequate contact time, the right environmental conditions and a microbial population equipped with an appropriate set of enzymes.
