The Shortage of drinking water supply arises due to 

- the world climate changes

- falling of ground water level

- high and increasing rate of evaporation 

- scanty and irregular rainfall

- lack of rivers and lakes

In Portugal particularly, in April 2019 a third of the country was in a state of severe meteorological drought.

Data collected from 

http://www.ipma.pt/pt/oclima/observatorio.secas/pdsi/monitorizacao/servico.situacaoatual/

*Index PDSI (Palmer Drought Severity Index))

In many parts of the world (including sub-Saharan Africa, Middle East, and Southern Europe), countries suffer from temporary but frequent water shortages.

Although low precipitation is often seen to be the biggest cause for these water shortages, inappropriate water-pricing systems cannot be overlooked since they cause excessive use of water.