Nothing is more useful than water. Ironically, hardly anything can be obtained in exchange for water. On the other hand, diamonds have little use, but a large amount of other goods and services may be obtained in exchange for diamonds. This apparent contradiction, known as the "Diamond-Water Paradox", was discussed by Adam Smith in his magnum opus titled "An Inquiry into the Nature and Causes of the Wealth of Nations". Smith stumbled upon the Diamond-Water Paradox whilst attempting to formulate his theory of value. He decomposed the word "value" into two parts: "value in use" and "value in exchange". Water has a high value in use, but a low value in exchange; diamonds have a low value in use, but a high value in exchange. Carl Menger and William Stanley Jevons later showed that value in exchange, or market price, depends not on the total usefulness of a commodity, but rather on its additional usefulness. The total usefulness of water is greater than that of diamonds. However, the usefulness of each additional glass of water is less than the usefulness of each additional diamond. This is because we consume so many glasses of water that each additional glass does not seem to matter much to us. On the other hand, we do not purchase as many diamonds, and so each additional diamond means a lot to us.

Although the Diamond-Water Paradox has been largely resolved, there are serious implications of a beautiful rock being more expensive than an indispensable liquid. This is because market price affects our perception of relative importance, and our perception of relative importance ultimately influences what we save and what we squander. Thus, diamonds are highly prized in society, but water is often wasted. While it may be common to exchange diamond rings during marriage, an exchange of glasses of water for the same purpose would be utterly inconceivable. We tend to feel at ease exchanging ornamental diamonds while allowing life-giving water to go down the drain.

The Sustainable Development Goals (SDGs) acknowledge the importance of water in human development. SDG 6 calls upon countries to "ensure availability and sustainable management of water and sanitation for all" by 2030. Access to "at least basic drinking water" refers to the availability of drinking water from sources such as piped water, boreholes or tube-wells, protected dug-wells, protected springs, and packaged or delivered water, whose collection time, including queueing, does not exceed 30 minutes for a round trip. The percentage of the population using at least basic drinking water services in Bangladesh increased from 95.60 percent in 2005 to 97.32 percent in 2015. Unfortunately, there was almost no improvement in access to safely managed drinking water, over the same period of time.

Apart from access to drinking water, SDG 6 also emphasises the importance of sanitation. SDG target 6.2 aims to achieve access to adequate and equitable sanitation and hygiene for all by 2030. Access to "at least basic sanitation" refers to the availability of sanitation facilities such as flush or pour flush to piped sewer systems, septic tanks or pit latrines, ventilated improved pit latrines, and compositing toilets or pit latrines with slabs, which are not shared with other households. According to data from the global database of the WHO/UNICEF Joint Monitoring Programme for Water Supply, Sanitation and Hygiene, the proportion of the total population in Bangladesh with access to basic sanitation services increased from 25.3 percent in 2000 to 46.9 percent in 2015. Additionally, the gap between rural and urban sanitation access also narrowed over the years. For example, in 2000, rural areas had 20.16 percent less access to basic sanitation compared to urban areas, but in 2015 this difference was reduced to 10.26 percent. In terms of geographic differences, Chattogram division had the highest and Barishal division had the lowest access to basic sanitation in 2015. Improvement in access to basic sanitation means that open defecation has been virtually eliminated from Bangladesh, even from rural areas. In 2005, the percentage of the population practicing open defecation was 11.91 percent nationally and 14.96 percent in rural areas. However, by 2015, the percentage of the population practicing open defecation fell to 0.10 percent nationally and 0.16 percent in rural areas.

Despite the progress made in improving access to water and sanitation in Bangladesh, a number of key challenges still remain. These include, inter alia, widespread inefficient use of water, lack of sustainable management of surface and ground water, low wastewater treatment, high levels of water pollution and poor quality of water. Additionally, lack of drinking water and sanitation facilities are reducing the efficacy of education and healthcare services where they are needed the most. Furthermore, inequalities are present in access to water and sanitation between urban and rural areas, as well as between slums and formal urban settlements. The existing pricing scheme used by the Dhaka Water and Sewerage Authority (WASA) is based on a single water meter for an entire building, and so does not create incentives for economical use of water by individual households. The poorest households in the capital city have limited access to water, and are often compelled to obtain water from illegal water vendors at exorbitantly high prices. In order to achieve SDG 6 by 2030, these challenges need to be tackled urgently by adopting sustainable integrated water management practices that consider both current and future needs of water and sanitation.

Syed Yusuf Saadat is Senior Research Associate at Centre for Policy Dialogue.