Letters | Why Covid-19 means Hong Kong needs more seawater in the flush

With rainfall low and Covid-19 increasing water demand, every drop of fresh water saved helps

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Clear Water Bay in Sai Kung, Hong Kong. Flushing with seawater saves the city up to 300 million cubic metres of fresh water a year. Photo: Dickson Lee

Published: 6:25am, 12 Oct 2020Updated: 6:25am, 12 Oct 2020

Hong Kong’s water consumption this year will be higher as we have all been washing our hands and cleaning floors etc more frequently since the first outbreak of Covid-19. Such precautionary hygiene measures are essential in a pandemic. However, we should not overlook the additional stress being put on Hong Kong’s water supply.

According to the Water Supplies Department, the city’s fresh water consumption for the first eight months this year was 678 million cubic metres, up 2.6 per cent year on year. However, the Hong Kong Observatory revealed that accumulated rainfall for the same period was 19 per cent below what it considers normal.

So, while the city’s fresh water demand is expected to stay higher for some time, water supply from rainfall has fallen. The city is facing water stress conditions. As with other strategic commodities, the city needs to balance its water supply and demand.

Climate change and pollution are adversely affecting water supply worldwide, and this will include Dongjiang, the major supplier of water to Hong Kong. Everyone needs to make a responsible effort to conserve fresh water. Our government and building owners must reduce wastage by properly maintaining public and private water pipes and increasing the use of lower grade water (seawater and recycled water) in non-potable applications such as flushing.

Hong Kong is probably the first city in the world to systematically use seawater in flushing, having started in 1957. This is estimated to save about 300 million cubic metres of fresh water a year, about 20 per cent of the total supply.

According to the Water Supplies Department, 0.606 kilowatt-hour of electricity is consumed to treat a cubic metre of fresh water whereas only 0.368kWh is needed to treat the same amount of seawater. The potential for energy saving and carbon reduction is noteworthy.

It is a no-brainer for the city to expand the seawater flushing scheme beyond the current 85 per cent of the population. Those whose buildings still use fresh water for flushing are paying more for their water supply. To encourage residents to make the “green” move, the department should consider waiving the seawater connection charge.