Customers of hydrosols should always demand a "Certificate of Naturalness" from the supplier. This will have a section showing the total percentage of the natural involved, and a listing of the percentages and identification of each additive, if any. If the product is truly 100% botanically derived from the named source by a purely physical process (i.e. steam distillation) then it will indicate this fact - If the supplier is unable to do this, change to someone more professional [a template of a typical Naturalness certificate is available from Cropwatch on demand].

Some genuine 100% natural hydrosols are storage-stable, and the natural bacteriostatic/fungicidal properties associated with many essential oils are enough to maintain product integrity (for a short shelf-life period at least). However, wherever natural products with a high water content are produced, opportunistic micro-organisms may become problematic. Those of you who have experience of brewery, potable water or dairy work will know that problems can occur which can be very difficult to eradicate. It is also true that the essential oil in some hydrosols only show weak anti-microbial properties. The upshot of this situation is that individual floating colonies of (often gelatinous) opportunistic fungi are frequently seen in hydrosols. This situation may require producers to add preservatives, stabilisers, anti-oxidants etc. to maintain the product in a fit state for later usage - these should be clearly stated on the label/accompanying literature or on the producer's website.

Returning to the specific question, the water content "as is" should be regarded as natural, and part of the product produced by an allowed physical process. It is true that more unscrupulous producers may physically add distilled or de-ionised water to adulterate the product - added water here would not be regarded as part of a natural physical process.

Be aware also that a carcinogenic group of compounds known as chloropropanols can be generated by steam distilling proteinaceous material (as would be found in the aromatic leaves, stems, roots etc. of plants) with chlorinated mains water. Many specifications now stipulate a maximum chloropropanol content (especially 3-MCPD) for essential oils (there is an EU limit for foodstuffs) although the problem is particularly associated with products like soy & oyster sauces, or with sterilisation of herbs etc.