Ndakaini Dam has enough water to serve Nairobi until June.
"The dam is full and overflowing," manager Job Kihamba told the Star on Tuesday.
This is good news for city dwellers as weather forecast for January indicates that most parts of the country will experience dry conditions.
The long rains usually begin in March or early April.
"We are doing conservation efforts by building gabions in some of the rivers supplying water to the dam to avoid soil erosion and siltation," Kihamba said.
The dam can store 70 billion litres at full capacity. It is 2,041 metres above sea level and 65 metres deep.
The facility, situated in Murang'a county, is the main supplier of water to Nairobi, which has a population of 4,397,073 people according to the 2019 census.
It is situated in a deeply incised valley of the upper Thika River near Ndakaini.
Earlier, Kihamba had told the Star that water infrastructure needs to be upgraded every 10 years as the city's population grows.
It is projected that Nairobi's population will hit 10 million by 2030, further straining the water infrastructure.
Nairobi City and Water Sewerage Company supplies 526.6 million litres per day from Ndakaini Dam.
This is against a demand of 800 million litres per day, leaving a shortfall of 273.4 million litres.
Edited by Josephine M. Mayuya