Earth or the fact that sustainable exploitation

Earth surface is about 2/3rd oceans and seas, and 1/3rd land. However most of this water is saline (sea water) and not fit for human use. Less than 3% of world’s water is fresh, and unevenly distributed – about 2% of water is frozen in Antarctic and Arctic, leaving only 1% of water readily accessible for human use, most of this 1% in turn is present underground as illustrated in Figure 1. Hence fresh water is a scarce resource which humans need for agriculture, industries and most importantly domestic use. This has been reiterated by many groups, most recently by World Economic Forum in their Global Risks Report 2017.As the urban population grows, so too does the number of people living in settlements that are not connected to a formal piped water supply. Their lack of access to clean water carries enormous health consequences. Urban water challenges can be divided into three categories:? Securing adequate supply of water for the cities;? Distribution of water? Treating used water from cities.5.2. STRATEGY5.2.1 WATER SOURCES FOR CITIESCities get their water from various natural fresh water bodies such as rivers, lakes and underground acquirers. Drawing water from surface bodies such as rivers is the simplest, so it is no coincidence that most of the cities in the world are located on river banks. Some relatively new ways in which cities meet their water demand is through desalination and waste water reuse.To summarise, the possible water sources for an urban area are:? Rivers and lakes;? Underground aquifers (also called underground reservoirs);? Waste water reuse;? Desalination.Underground aquifers are a good source but withdrawal rate is greater than recharge rate leading to drop in water tables. Desalination is expensive and energy intensive. Increasing water efficiency and decreasing the losses in transportation, coupled with waste water treatment and possible reuse are promising solutions to provide all urban dwellers with sufficient water services.5.2.2 WATER DISTRIBUTION AND WATER COLLECTION ACTORSAs the cities grow, urban water managers are facing increasingly complex, multifaceted challenges such as growing social expectations or the fact that sustainable exploitation of natural resources has reached its limits. Cities must be able to actively intervene in thecatchment scale management in order to improve long-term access to water (Martos et al., 2015).The water distribution and waste water collection within a city can been seen as a network considered “life-line” of many cities, as they deliver safe and clean drinking water to business and homes and also, collect waste water (contaminated water) for its safe disposal.Current models of urban planning and water management have already failed or likely to fail from the perspective of cost effectiveness, technical performance, social equity, and environmental sustainability.5.2.3 DISTRIBUTIONS SYSTEMSLeaks in the distribution and collection of water network is one of the principal problems water managers in cities have to attend as a priority. For instance, 32 billion cubic meters of water a year is lost due to leaks in water mains around the world. This means that 25% of all urban drinking water is lost (Unesco, 2014).In the USA, biggest consumer of water per capita, every day 22.3 million cubic meters is lost due to leaks, which is more than enough to provide of water to the 10 largest cities in the United States (Unesco, 2014). In some developing countries, up to 50 percent of water is lost in the journey from treatment plant to household tap (Shugart, 2016).A study of leak detection technologies in water distribution networks was undertaken in Canada to provide an accurate assessment of the pipe condition in all such cases, but no single method is capable of resolving all the problem on its own.To address this problem, a hybrid approach was proposed, which integrates acoustic and electromagnetic-radio frequency technologies (Zahra Zangenehm Adar, 2014).This is no small investment. The World Bank has estimated that this can cost around US$2.9 billion annually and taking into account that the Water Distribution Network (WDN) reported to be the most expensive part of water supply systems but fixing the problem could provide water for 90 million people without requiring one drop of additional water (Shugart, 2016).Some innovate leak detection tools are in the market like Smartball, which consists of a range of sensors such as magnetometer, ultrasonic transmitter, accelerometer, temperature sensors and a power source.5.2.4 COLLECTION SYSTEMSThere are many opportunities where reducing water usage from domestic areas lower the charge of collection system. This represents two main challenges, the first a big change in existing configuration of the water network. This means that actual sewage systems in average cities where separation of waste water like grey-water, black-water and also rainwater cannot be done due to old sewage network. Second important challenge is the investment needed.One first step would be the implementation of low flush toilets, low consumption laundry equipment and efficient shower heads. The installation of more efficient water fixtures and regularly checking for leaks will reduce daily indoor per capita water. 60% of indoor water use is attributed to toilets and shower heads, a major source of inflow into sewer networks comes from domestic (sanitary) wastewater.Second step, is the emergence of source-separated sanitation system from new-urban areas. This means separate systems for grey-water (wastewater generated from water use activities in the kitchen, hand, washing, showering and laundry), and black water (wastewater collected from toilet including urine, faeces, toilet paper and flushing water), which would be collected and transported in separate pipes. This is claimed to result in a number of benefits that with help in progress towards sustainably, like:? Improved recovery of energy, nitrogen and phosphorus, as the wastewater is more concentrated and wastewater streams are more homogenous(Roefs et al.).? Improved properties for reuse of black water sludge in agriculture, because contaminations with heavy metals is low, as they are primarily from dietary source(Roefs et al.).5.2.5 WASTEWATER TREATMENTLocal water reuse approaches that permit safe and productive re-use within domestic, industrial and (urban) agriculture systems have the potential both to increase the available water and to reduce the operational costs for treatment.The recycled wastewater can be used for irrigation, landscaping, industry, and toilet flushing. Also, there are other uses, such as, to replenish sensitive ecosystems where wildlife, fish and plants live.There is a scarcity of innovations that promote increased recycling of wastewater and ensure that water can be used many times, by cascading it from higher to lower-quality uses.Energy-efficient treatment has also been developed around natural systems that are capable of removing multiple contaminants in a single process. Innovations in this area include constructed wetlands, soil aquifer treatment and river/lake bank filtration.Different technological stages used to recycle and purify water:1. Sewage goes through advanced primary treatment and water is separated from large particles. Then, water enters sedimentation tanks where chemicals are used to make primary sludge settle to the bottom and scum rise to the top. Afterwards, water can be discharge to a large water body such as a lake, a river or the ocean.2. If the water is needed with a higher level of purification bacteria is added to ingest organic solids that produces secondary sludge.3. Afterwards, water is filtered to remove any solid that remains. Chlorine can be added to disinfect the water.4. Then if water is desired for home usage undergoes advanced water technology can be complemented to the chain, water spends some time in groundwater or surface water bodies, such as reservoirs, before being sent to drinking water supplies.Advanced water technologies involve microfiltration that strains out any remaining solid.5. Reverse Osmosis applies pressure to water on one side of a membrane allowing pure water to pass through, eliminating bacteria, viruses, protozoa and pharmaceuticals. Next, the water is then disinfected by ultra-violet light (UV), ozone or hydrogen peroxide.As a final stage, water is added to the groundwater or surface water bodies, where it stays more than 6 months to be further purified by natural processes.5.2.6 HOW IMPORTANT IS WATER SAFETY AFTER TREATMENTUnsafe water and inadequate sanitation and hygiene are significant contributors to the 1.8 million deaths caused by diarrhoea every year. For children under five years of age, this burden is greater than that covered by HIV and malaria combined. Water transmits disease when it is contaminated by pathogenic microbes and/or chemicals. Bacteria, viruses and parasites can enter drinking water in many ways, for example as a result of animals excreting in to a catchment area, from seepage of contaminated water into ‘leaky’ pipes in a distribution system, and from unhygienic handling of stored household water. Chemical contamination may come from natural or human sources.5.2.7 SOLUTIONSProtecting source water from pollution is critical. Households and water treatment plants can avoid most disease and poisoning through ‘safe-water’ approaches, by drawing on a well-managed supply system or by treating and safely storing water at home. Such interventions are most effective when coupled with improved sanitation and hygiene (including food) to ensure the multiple pathways of disease transmission are prevented.Improvements should be made for the scaling up of household water treatment and safe storage in places where water supplies do not deliver safe water, or where water is subject to recontamination during collection, transport and storage in the home.Nearly half of the developing world’s population receives water from a piped supply that is frequently unreliable and contaminated. The World Health Organization assists suppliers to better manage their systems by working with partners, like the International Water Association, the Australian Government Overseas Aid Program, the Japan Ministry of Health, Labour and Welfare, and the UK Department for International Development.