The cost of water treatment in Kigali city could rise if flooding of Nyabarongo River, occasioned by heavy rains, persists, Water and Sanitation Corporation (WASAC) has said.

The warning comes after Nyabarongo River upper catchments experienced heavy flooding last week, disrupting activity at Nzove water treatment plant and reducing its production by nearly a half, WASAC said.

This has caused a shortage of water supply in parts of Kigali.

The plant, which produces 1950 cubic meter per hour, treats water from Nyabarongo River.

Due to flooding, WASAC says, the plant now produces 1050 m3 per hour, 50 per cent of its capacity.

The floods, usually characterised by soil erosion from agricultural activities, artisanal mining zones and un-tarmacked roads in surrounding areas affects Nyabarongo River.

Aimé Muzola, the Chief Executive Officer of WASAC, told The New Times that if the problem continues, it will increase the cost of treating water.

"The high cost of treating muddy water could increase water tariffs,” he said.

This comes after prediction by Rwanda Meteorology Agency in September this year suggested that due to high rainfall, most parts of the country would  experience flooding, which it warned would affect infrastructure, including hydropower and water treatment plants.

"Due to heavy rain last weekend, we are experiencing a problem of turbidity at Nzove water treatment plant. As (an) effect we can't treat water as usual. This problem affects water supply for a big part of (the) City of Kigali,” WASAC said in a tweet.

This is the second time the Nyabarongo River is flooding in a space of four months.

The same issue happened in September this year, causing water shortages in many parts of the city.

WASAC warned that areas likely to be affected include Nyarutarama, Kibagabaga, Bumbogo, Gihogere, Rukiri, Ruturusu, Nyagatovu, Nyabisindu, Bibare, Rwimbogo, and Gasaraba.

Although the situation was normalising, there was need for a long term solution to control flooding of Nyabarongo River, Muzola said.

"Because Nyabarongo upstream and catchments are not protected enough against erosion, soil and mud are washed away by flooding into Nyabarongo River which becomes too muddy. This hampers water treatment plant turbidity as it loses capacity to continue treating water. This requires joint efforts to seek long-term solution,” he said.

Sometimes they are forced to switch off the plant for about two hours a day, he said.

"But because we have other different sources of water supply such as Kanzenze, all areas are not affected at the same time,” Muzola added.

Floods have also halted activity in water treatment and hydropower plants in other parts of the country.

For instance, two power plants, Gisenyi and Gihira in Rubavu District are often affected due to flooding around Sebeya River.

Gihira treatment plant, which produces 8,000 cubic meters of water every day, is also vulnerable to erosion, sometimes forcing it to suspend activity for five hours every day.

The plant reportedly loses an average of Rw20 million every heavy rainy season.

Meanwhile, Muzola said that they have temporary solutions to limit the shortage of water supply although he added that long-term solutions are needed.

"We have reservoirs that supply water when there is no water from the treatment plant,” he noted. "But when there is delay in normalising the situation water from reservoirs can get exhausted and some areas can be affected.”

WASAC says that it is building more water reservoirs in Kicukiro, Busanza and Gasanze to cushion the city against further shortages.