The Zimbabwe Meteorological Services have predicted that this rainy season will most likely be a short one, so Harare’s water woes are not going to get any better. Because of perennial water shortages, residents need to seriously consider collecting rain water run-off as a solution to domestic water scarcity.
According to Dr Peter Morgan, a Harare-based rain water engineer, low-cost technologies need to be developed particularly in light of the decreasing amount of rainfall each year. Morgan explains that while gutters on the roof of a house are commonly used to collect rain, it is preferable to use a plastic sheet collector suspended from four posts. It should be fitted with a downpipe and a stainless steel screen. It can be detached from the posts and stored. Another way is to place a bucket with a screened outlet beneath the end of a sloped gutter permanently fitted to the roof. In each case the rain water is led from the collecting surface to the storage tank through a 25mm plastic pipe.
For roof catchment, only the portion of the house roof which is away from trees should be used to reduce the build-up of leaves and other foreign matter. Dr Morgan also notes that it is desirable that the gutter system is detachable, so it can be removed, thoroughly examined and cleaned easily before water collection. It should also be set to have a slight slope to improve water flow.
“We used to collect water from the roof on our stand in Marlborough. The roof is by far the largest surface available for rainwater catchment in any homestead but I have always worried about the quality of the water collected from roofs using standard guttering. Roofs get dirty and contaminated, as do the gutters which carry the water to the storage tanks. Also, storage tanks can themselves become contaminated if they are not well sealed and the water that flows into them is not screened,” said Dr Morgan.
He explains that the restricting factors may be the cost of a suitably sized storage tank, the careful use of the water collected and also the bacteriological safety of the water. Rainwater collected from dirty roofs and gutters and tanks which is not cleaned and sealed can easily become contaminated.
“Meticulous care is required to keep roof collectors and gutters clean and tanks well sealed. Without proper care, small animals can be washed down gutters and fall into unsealed tanks, where they rot. The first rains collected from roofs should not be used. Only after the first few showers after the system has flushed through,” says Dr Morgan.
For the past 40 years, Dr Morgan has been working to bring both clean water and improved sanitation to rural communities around the world, helping millions of people along the way. He was honoured for his work when he won the 2013 Stockholm Water Prize in recognition for his simple, innovative ways of harvesting rain water.
Dr Morgan adds that it is worrying that water tables are receding year by year in the city. “In a study conducted in Epworth and in Marlborough I began taking water readings for rainfall and the water table at the beginning of last year (2014). During 2014 our own tube-well had shown signs of drying and the other well had already dried. This was thought to be caused by a combination of lower than average rainfall and also a higher rate of ground water extraction by many new boreholes sunk in the area – a common trend in Harare. Many of these supply and deliver water on a commercial basis to provide families with water,” he said.
Another water expert, Innocent Nhapi concurs that alternative ways of trapping rain water are critical as ground water tables are dwindling fast. He says on a broader scale, the preservation of wetlands, which recharge ground water, should also be taken seriously.