Water, which is most of the bottle

The largest ingredient by a long way, the cheapest, and the one that causes the most trouble when it is not thought about.

Ninety percent of the product

A ready-to-use cleaner is typically 90 to 99 percent water.

Which means water quality is a formulation variable rather than a detail, and it means the shipping economics are mostly about moving water.

Why tap water is a problem

Hardness, which consumes anionic surfactant and precipitates soap scum, and varies by region and by season.

Metal ions, which degrade some ingredients and reduce preservative efficacy.

Microbial load, which is low in treated supplies and is not zero, and which inoculates the batch on day one.

Chlorine, which can react with fragrance and dye and produce an off smell.

A formula developed on tap water in one location is a formula that has an unrecorded ingredient in it.

What to use

Deionized or distilled water for anything sold, as standard. It removes hardness and metals and it makes the formula reproducible anywhere.

It is inexpensive at small scale and available in bulk at larger scale, and a small deionizer pays for itself quickly.

Whichever you use, record it on the formula sheet. "Water" is not a specification; "deionized water" is.

And keep it clean: a storage container of deionized water left open is a microbial culture, and it will seed every batch made from it.

The shipping consequence

Shipping a ready-to-use cleaner is mostly shipping water, and water is heavy and worth nothing.

Which is the entire commercial argument for concentrates, and it is a real one: the same cleaning performance at a fraction of the freight, the packaging and the shelf space.

The counter-argument is that the customer has to dilute correctly, with their own water, which brings the hardness problem back.

References