A crucial water issue plaguing river valley settlements in south Asia is ground water contamination by arsenic and fluoride. Implications of large scale contaminated ground water usage include contaminated food chain and increasing vulnerability to metalloid poisoning.

Dear Nicolas,

Unfortunately, problems often fall into a general category. In my humble opinion, or the problem may be detachable.

I think the main problems are: erosion, flooding, water pollution, water scarcity, and over exploitation of water resources.

My top 5 would be

1. Water Availability (Lack of infrastructure)

2. Waste Water Treatment or Lack of

3. Water Pollution (Arsenic, Heavy Metals, Human Waste)

4. Flash Flooding (extreme weather events)

5. Lack of Trans-Boundary Water Governance

But you must know all these factors are interlinked to a degree where no one can be addressed alone.

In my opinion the top 5 issues in Africa are:

1. Desertification

2. Uncontrolled deforestation of tropical wet forests

3. Exploitation of precious minerals in South Africa which affect local communities and forests

4. Poaching

5. Problem of drinking water in many countries from Central Africa and  North East Africa

In my opinion the top 5 issues in Asia such as:

1. Typhoons - natural hazards

2. Earthquakes

3. Exploitation of hydrocarbons and other minerals

4. The air pollution in big cities Beijing, New Delhi - of petrochemicals the processing in such economies leading to the accumulation of aerosols in the atmosphere, which are fine particles suspended in air.

5. Uncontrolled deforestation of tropical wet forests

A very good and practical question. After reading above replies, I support @Raoof. He has given a very precise, accurate and to the point answer.

I do appreciate the previous answers. Among many issues regarding water related environmental crisis in Africa, and Asia, as @Raoof have mentioned is WATER SCARCITY! Please, have a look in a map and focus on blue colour of African continent depicting Economic Water scarcity!

Global Drylands is also a lack of water issue!

http://www.un.org/waterforlifedecade/scarcity.shtml

http://www.zaragoza.es/ciudad/medioambiente/onu/en/detallePer_Onu?id=39

I think that the main problems are water scarcity and water-related deceases.

In Africa, almost half of the population suffers from one of the six major water-related diseases, such as diarrhoea, which kills millions of children worldwide millions every year.

One in five developing countries will face water shortages by 2030. The Near East, North Africa and parts of Asia are subject to water scarcity and stress.

http://wwf.panda.org/about_our_earth/top_5_environmental_questions/faq_freshwater_q_a/

Bonjour Nicolas

le fleuve Congo représente la plus grande réserve d'eau de surface d'Afrique, et pourtant les pays qui le bordent ne peuvent assurer l'alimentation en eau potable à toutes leurs populations. Ceci constitue en soi une situation de crise majeure, et pourtant si facilement solvable avec des investissements adéquats...

Global water shortages to deliver 'severe hit' to economies, World Bank warns!

The Middle East, north Africa, central Asia and south Asia due to suffer biggest economic hit from water scarcity as climate change takes hold, report finds.

"Water shortages will deliver a “severe hit” to the economies of the Middle East, central Asia, and Africa by the middle of the century, taking double digits off their GDP, the World Bank warned on Tuesday.

By 2050, growing demand for cities and for agriculture would put water in short supply in regions where it is now plentiful – and worsen shortages across a vast swath of Africa and Asia, spurring conflict and migration, the bank said.

Water shortages could strip off 14% of GDP in the Middle East and nearly 12% of GDP in the Sahel – without a radical shift in management, according to the bank’s projections.

Central Asia could lose close to 11% of GDP and east Asia about 7% under business-as-usual water management policies, according to a new report.

Taking into account all regions, the mid-range toll of water shortages on GDP was about 6%..."

https://www.theguardian.com/environment/2016/may/03/climate-change-water-shortage-middle-east-asia-africa-world-bank