What we measure
Dam storage figures — the percentage of each dam’s capacity that is full, and the total stored across the six major dams of the Western Cape Water Supply System, the set of dams that supply Cape Town. A dam’s percentage is simply the water it holds divided by its full supply capacity (City of Cape Town’s own explanation of its table). We publish one combined figure and, on dam pages, per-dam figures.
We do not forecast. No “dams will be at X by summer” — from us or from the card. The Water Desk covers water status only.
The verdict bands, published
The briefing card’s verdict line is selected from the band table below, frozen for launch. A band is the year-on-year change in percentage points, taken from the same source’s own year-ago column. This is CTIA’s own editorial classification of the measured number — not an official threshold and not a warning system.
Verdict bands, frozen for launch| Band | Year-on-year change | Verdict line |
|---|
| Above | +3.0 points or more | “Dams sit above the same week last year.” |
|---|
| Close | −3.0 points up to, but not including, +3.0 | “Dams sit close to the same week last year.” |
|---|
| Below | −10.0 points up to, but not including, −3.0 | “Dams run below the same week last year.” |
|---|
| Well below | below −10.0 points | “Dams sit well below the same week last year.” |
|---|
Two storage modifiers sit on top of the bands when the card renders: when storage is below half, the verdict line gains “…and storage is below half.”; when storage reaches 95%, the card says “Dams are close to full.” instead. Some bands add a quiet sub-line — “A comfortable margin for this time of year.” above; “Not dramatically — but the gap is real.” below; “The gap is wide enough that every litre counts.” well below.
Which dam set am I looking at?
Dam percentages depend on which set of dams you count, and there is more than one set in circulation: the City’s six major dams; the City’s wider “Big 5”/“Big 6” shorthand; and DWS’s full Cape Town system, which adds smaller dams, including balancing dams whose levels swing by design. We label which set a number belongs to, every time — and we keep “Big 6” out of our headlines, because on this site “Big 6” already means the city’s famous attractions.
Why two sources sometimes disagree
They measure on different days (DWS surveys on a fixed weekly date; the City reads daily), and their capacity totals differ slightly because the dam sets and survey methods differ. On adjacent dates in late October 2026, for example, DWS read Voëlvlei at 55.1% and the City read it at 55.0%; for Wemmershoek, 81.9% against 79.4%. Both are correct; they are not the same measurement. Our rule: never mix sources in one figure, and prefer the City for the six-dams story and DWS for the whole-system story.
How the year-on-year comparison works
When the card says “the same week last year”, it uses the same source’s own year-ago column — the City’s “% 2025” column or DWS’s “Last Yr” — never a figure assembled from two sources. Our own archive of daily snapshots starts the day this desk launched, so it is too young to back-check a year-ago column yet. Once the archive spans enough dates, including a full year boundary, we will turn that cross-check on and note it here. For our own historical charts (from v1.1), we compute from the historical tables, not from mixed sources, and label the comparison “same week last year”.
What the numbers cannot tell you
- Dam percentage is not household reliability. Whether water reaches your tap depends on the City’s distribution network, tariffs and restriction decisions — none of which are in these numbers.
- The figures exclude groundwater, reuse, desalination and other augmentation. The City covers those separately in its Water Outlook reports.
- A weekly citywide demand figure is not available from any public machine-readable source we could verify; the published suburb consumption data is a monthly median for single-residential accounts and cannot be added up into a city total. So we don’t publish one.
- A “days of water left” countdown needs assumptions we won’t hide. If such a projection ever appears on this desk, it will label its assumptions, not just its data.
- Historical corrections happen. DWS keeps corrected history in its verified-data portal rather than editing old bulletins; older figures can be revised.
Seasonal context (method, stated up front)
When we place a figure in seasonal context, we use the median of the same week over the last ten complete years from one source’s own history, and we name the years. Median, not average — drought years distort averages.
Cadence and maintenance
- Cadence: dam figures refresh daily around 06:00; the weekly wrap publishes Fridays at 09:00 (published cadence, matches the actual job schedule).
- Who maintains this desk: the weekly wrap is written and approved by Quill (CTIA editorial); Mira holds the verdict wording and acts as backup. The daily pull is automated; nothing on the card is auto-written prose.
- Corrections: we treat water figures like any other fact we publish. Spotted something wrong? Email info@capetownisawesome.com and we will fix it and record the fix. For water faults and restrictions, the City’s own lines are faster: water@capetown.gov.za / 0860 103 089.
Licensing posture
We link rather than republish: the City’s website content is copyright of the City, and we point to the source page for anything beyond figures; we re-present the numbers with attribution. DWS publishes no explicit reuse licence for its bulletin; we attribute every DWS figure by name and link the bulletin.
Sources