Does a Callander water-treatment specialist hold specialized knowledge for L-1B purposes?

Only if the knowledge is of her employer's own method rather than of water treatment generally. Special knowledge of the organization's product, service, techniques or processes qualifies; advanced professional skill that a competent engineer could acquire elsewhere does not. The distinction has to be drawn explicitly in the petition.

Name what only this company knows

Hypothetical example: Yusra is a water-treatment process specialist at a Callander environmental-services company. The weakness in most specialized-knowledge petitions is that they describe an excellent employee rather than a distinctive body of company knowledge. The stronger approach separates two things.

Industry competence covers what any qualified process specialist understands: fouling mechanisms, chemical compatibility, standard cleaning cycles. Company knowledge covers what exists only inside this organization: the protocol it developed and revised over years, the diagnostic thresholds it set from its own plant data, the sequence it validated, and the internal documents in which all of that is recorded. Yusra qualifies on the second, and the petition should show it by pointing at documents rather than adjectives.

Evidence that she wrote or maintains the method, that colleagues are trained on it internally, and that customers buy it as part of the service, is worth more than any description of how experienced she is. Where colleagues elsewhere in the company could perform the same work, that fact should be surfaced and explained rather than avoided, since a careful reader asks it first.