The theme of ‘World Water Week – 2022’ was

Concept — A water observance is identified by the theme its organising body announces for that particular year; the theme sets that year's policy focus and is not the same thing as a general conservation slogan. Two observances are routinely mixed up: World Water Day, held on 22 March under UN-Water, and World Water Week, the annual conference convened in Stockholm by the Stockholm International Water Institute (SIWI). Each announces its own theme, and the two themes for a given year are different.

Applying it here — The question asks about World Water Week, that is the SIWI conference, whose 2022 edition ran from 23 August to 1 September 2022. SIWI announced its theme as “Seeing the Unseen: The Value of Water”, directing that year's programme at water which is invisible or unaccounted for — groundwater, the water embedded in food and energy supply chains, and the social and cultural worth of water — and at how that value should be weighed in decisions.

Cross-check — Anchor the theme against its neighbours so the recall stays reliable:

• World Water Day 2022, on 22 March, ran under a different theme: “Groundwater: Making the Invisible Visible”. Both 2022 themes point at water that is not seen, which is precisely why the two events get swapped — match each theme to its own event.

• “Preserve water – Preserve Life”, “Think before you let it drop” and “Drip, Drop, Drip, Drop. This Clock must be stopped” are general water-conservation slogans of the awareness-poster kind; none was announced as the World Water Week 2022 theme.

So World Water Week 2022 was held under the theme “Seeing the Unseen: The Value of Water”.