The New Nation - Internet Edition

Sifat MunimTanin

Rain water is a free source of nearly pure water. It can be used to supply potable (drinkable) water and non-potable water. For non-potable uses, like watering landscapes, it is ready for use as it falls from the sky. For potable uses, rain water must be treated to remove or kill disease organisms that may be present.

This process in one form or another - has been in practice for thousands of years. According to Paul Woods of Texas A & M University, extensive water harvesting systems in the Negev Deserts of Israel more than 2,000 years ago have been documented. Additionally, Roman villas and cities were planned in such a way to take advantage of rainwater for drinking and air-conditioning. Cisterns, containers to collect rainwater, were fairly common in the United States in rural areas until the 1920s.

In Bangladesh the amount of rainfall varies both spatially and temporally. While the maximum amount of average annual rainfall occurs in the northeastern districts (55 cm) of Sylhet and Moulivibazar, the minimum amount falls in the western/southwestern districts (15 cm) of Meherpur, Kushtia, Chuadanga, Chapai Nawabganj, Noagaon, and Rajshahi. Also, rainfall is mainly restricted during the months of April to September. Consequently, rainwater harvesting will be relatively easier during certain months of the year in the certain parts of Bangladesh. Groundwater contamination by arsenic is more severe in the western/southwestern districts, where rainwater harvesting would be more appropriate to solve the polluted drinking water problems. A 1982 study, by the United Nations Environment Program, showed that with an average rainfall of 72 inches and using 1,100-gallon storage tanks, enough water could be collected in 12 hours to serve a family of six for 45 days.

Rainwater collected in various parts of the USA contains (in milligrams per liter): Fe (0.015) , Ca (0.075-1.41), Mg (0.027-1.2), Na (0.22-9.4), Ca (0.075-1.41), K (0.072-0.11), HCO3 (4-7), SO4 0.7-7.6), Cl (0.22-17), NO2 (0.02), NO3 (0.02-0.62), and Total Dissolved Solids 8.2-38), and pH of 4.9 to 6.4. On the other hand, Bangladesh does not have such industrial establishment like other developed countries. Rainwater in rural areas - away from atmospheric and industrial pollution - is fairly clean except for some dissolved gases, it may pick up while traveling through the atmosphere.

But there are some specific problem for Bangladesh. First, there is no enough land for the development reservoir in Bangladesh. Second, reservoir may become polluted by surface runoff. It may carry different pollutant from non-point sources. Possible non-point sources of contamination include fertilizer, pesticides, chicken and cow manure, dissolved minerals, sediments, sewage, decaying plants, algae, bacteria, aerosol fallout, and detergents. Fourth, ponds may be connected to groundwater flow and may subject to contaminated by dissolved chemicals.

Now the supply of water is going to become a great problem in our country. We need to take proper initiative for the development of rain water harvesting process in Bangladesh.