İstanbul’s dams are well over half full.

61.5%Friday 6 November 2026, 00:00Measured 23 hours ago. Source: İSKİ.

That is about 534 million cubic metres of water.

About 38 mm of rain fell on the dam catchments over 27–29 October. A week ago the dams were 53.7% full.

We call 60–100% “safe”.

Height: share of total capacity. The red ▽ is today’s level, and the dotted lines tie each range to today’s surface. The triangles on the wall are the lowest points of past droughts; the filled one is the lowest day on record.

In 14 days 20 November: 64–77% most likely 68%
In 30 days 6 December: 64–91% most likely 76%

There’s an 80% chance the level stays inside each range.

Over the next month the water will most likely rise.

How well these forecasts hold up

The most likely level a month ahead has moved up 0.6 points since yesterday morning (76%, now 76%). Main reason: the new level reading.

4 forecasts have a result, and 4 landed inside the range. With so few, we don’t give a hit rate. In most of the 120 short runs we made in recent days, the model put the level higher than it turned out. Our value for a month ahead may be high too.

Hindcast: We re-ran 2011–2023, each time with only the data known on that day. The 30-day forecast was off by 3.7 points on average, and 82% of outcomes landed inside the range (the target is 80%).

The full scorecard

We make the forecast again every morning.

The live archive started on 19 October 2026. It holds 19 mornings’ forecasts so far. 7 days ago the most likely level a month out was 68%. In today’s forecast it is 76%. The forecast has moved up 8 points.

Each upright line is one morning’s forecast: the range we gave for 30 days later, with a short tick at the most likely level. The dark area is the measured level. Once a forecast’s date arrives, what happened is added as a filled triangle.

Every forecast and its result, on the Scorecard page

Rain in the next days

About 19 mm of rain is expected over the catchments in the next 14 days (6–51 mm). In the same days of the previous 26 years the average was 27 mm; the expected amount is below that.

The dashed band covers the 10th to 90th percentile of the 51 ECMWF members’ rain totals; the line in the middle is the median. The solid line is the average total for the same days in earlier years. Rain is the mean over the ten dams’ catchments (Open-Meteo), which reads a little below İSKİ’s rain gauges.

The city uses about 3.2 million cubic metres of water a day.

That’s enough to fill the Basilica Cistern 40 times over, every day.

In the past week the water in the dams rose by about 67.3 million cubic metres. That is what the city uses in 21.3 days.

The dams hold 868 million cubic metres when full. With no rain and nothing from the pipelines, the fill level would drop by about 0.4 percentage points a day.

İstanbul is not on a big river, so it stores rain. That is what cisterns like the Basilica Cistern and the Ottoman dams in the Belgrade Forest were built for.

Daily use is an approximate value read off İSKİ’s yearly charts. The Basilica Cistern holds about 80,000 m³ (yerebatan.com).

On 5 November 2007 the dams were down to just 80 million cubic metres.

It is the lowest day on record. The dams were 9.2% full. The level fell until this day, then rose again with the autumn rain.

Today the dams hold about 6.7 times as much.

The same drought ran on into 2008.

Some of the water at the bottom of a dam never reaches the pipes. İSKİ doesn’t say how much. A rule of thumb often quoted in the press is 10% of capacity. If İSKİ’s percentages already leave this water out, that share should not be counted. Until İSKİ tells us, we show both.

On this date the dams are fuller than in most years.

The record has readings for 6 November in 24 years. In 20 of them the dams held less water than today, and in 4 they held more. The last year they were fuller on this date was 2015 (68.4%).

There is no reading for this date in 2024 and 2025, so those years are left out of the comparison.

Pick a year. The water in the drawing moves to that year’s level on this date, and the red mark stays at today’s level.

2024: no reading
2025: no reading

Average 47.8%. Lowest 2007 (9.4%), highest 2009 (88.3%).

Water reaches the dams two ways and leaves them two ways.

Rain and the pipelines from the Melen and Yeşilçay rivers fill the lakes. The city’s taps and evaporation drain them. Rain is the least certain part of the sum.

Rain: Dry soil keeps some of it. The rest runs into the lakes. 27–29 October: about 38 mm.
Pipelines: About 1.4 million m³ a day. İSKİ decides how much.

The city: About 3.2 million m³ a day.
Evaporation: Water lost off the lake surface. More in summer.

Daily amounts are approximate, derived from the yearly totals İSKİ publishes.

Since 2000 the dams have fallen below 20% in 5 separate years.

Those years were 2007, 2008, 2014, 2021 and 2023. There are no readings between 2024 and 2026, so that part of the chart is empty.

How full İstanbul’s dams were, 23 October 2000 to 6 November 2026. The last reading of each week, plus every year’s lowest and highest day. 2000–2024: İBB Open Data. After that, İSKİ data via DSİ and dolulukorani.com.

Every year the dams fill in winter and drain in summer.

The lakes are usually at their lowest in November and their highest in April. That is why the year here starts on 1 October, as it does in the State Hydraulic Works’ (DSİ) accounts.

This year is 13.0 points above a typical year right now. In a typical year the dams are 48.5% full on this date.

The grey area runs from the lowest to the highest fill seen in each week across 23 years, 2000–2023. The dashed line is a typical year, the dark line this year.

Beyond a month, it depends on the weather.

Nobody can see the rain more than two weeks ahead, so the range widens the further out it goes. We draw it so there’s an 80% chance the level stays inside.

In past years the dams usually rose over the month after this date.

From day 30 to day 90 we replay past years’ weather over today’s lakes: if the coming months turn out dry like 2022 or wet like 2021, how much water is left? We sort the results by rain into dry, average and wet. Nothing past day 90 is drawn.

The solid dark area is measured water. The area shaded with fine lines, inside the dashed outline, is the 30-day forecast range, and the thin line in it the most likely value. After day 30 the lines are scenarios, and the range bars at their ends show each scenario’s range. Forecast issued on the morning of 6 November 2026, starting from the reading of 6 November 2026.

Dry: Day 90: 74–100%The 9 years with the least rain in this season: 2000, 2002, 2006, 2007, 2011, 2013, 2015, 2019, 2022.
Average: Day 90: 84–100%The 9 years with rain closest to average: 2003, 2004, 2008, 2012, 2017, 2020, 2023, 2024, 2025.
Wet: Day 90: 87–100%The 8 years with the most rain in this season: 2001, 2005, 2009, 2010, 2014, 2016, 2018, 2021.

Scenarios worked out in autumn show too narrow a range at 60 and 90 days. In the hindcast, 80% of outcomes should have landed inside. At day 60 it was 75%, at day 90 68%. What matters most is when the first big rain arrives.

The chart’s figures as a table

Days ahead	Forecast	Dry	Average	Wet
14 days, 20 November	64–77% (68%)	–	–	–
30 days, 6 December	64–91% (76%)	–	–	–
60 days, 5 January	scenarios only	69–92% (80%)	72–99% (87%)	86–100% (95%)
90 days, 4 February	scenarios only	74–100% (88%)	84–100% (96%)	87–100% (98%)

The scenarios in detail, and the transfer settings

We don’t give a date for when the water runs out.

Once rain and the pipelines are counted, no single date would be honest. That is also why the “days of water left” figures in drought reports rarely agree. We give only a range, with its assumptions beside it.

None of the three scenarios has the dams losing water over the next 90 days, so a “days of water left” count gives no number today.

Decisions such as water cuts, lower pressure or calls to save water are İSKİ’s, and İSKİ announces them. This page doesn’t know those decisions. It shows only the water in the dams and where it is heading.

The assumptions and the days per scenario are on the Scenarios page

Every morning we work the figures out again from the new reading.

Every figure on this page takes the same route. If a value was copied by hand from İSKİ’s page, the page says so.

If a step fails it runs again at 12:40. Times are İstanbul time.

All seven steps, with the state of each today, are on the Methods page

Where these figures come from

Latest reading: Friday 6 November 2026, 00:00
Source: İSKİ
Forecast: morning of 6 November 2026, from the reading of 6 November 2026
Updated: Friday 6 November 2026, 23:04
Model version: 2
Files: home.json, narrative.json, outlooks.json, story.json, dams.json, scorecard.json