For good and obvious reasons, destruction of essential civilian infrastructure such as water supply and sewage systems is prohibited by the laws of war. Attacking such targets is a war crime.
For Israel, it's not just a war crime. It's a strategy and it's called Dahiyeh. It's the deliberate targeting of civilians; their homes, schools and hospitals; and the water plants and sewage systems essential for public health and safety.
When Israel began waging Dahiyeh against Gaza Palestinians in July, it sent warplanes in to take down the water station and sewage plants. Now a group of 30-humanitarian agencies banded together under the name EWASH (Emergency Water Sanitation and Health) warns that two-thirds of the Gazan population is running out of water and the besieged territory is at risk of outbreaks of water-borne diseases.
Israeli destruction of Gaza's sewage infrastructure has led to broken mains and open sewage flooding.