Water, on Mars as on Earth, is essential to life and therefore to any Mars settlement. Water infrastructures, including water treatment facilities and water distribution systems will be part of any Mars settlement from day one. Indeed it will be part of the vehicles bringing the settlers to Mars.
Melting, crushing, transportation
Extracted water may contain contaminants such as dust, salts and other materials
Potable water may need biological treatment (chlorine).
Water may (will) be mixed with re-used water. There will be large amounts of water removed by dehumidification from greenhouses.
Water storage and distribution
Water is usually stored in tanks and distributed through pipes using pumps. Raw water is water that has been extracted, but not yet treated for use.
Water will be produced from two sources in a settlement. 1- Respiration and biological processes produce water through combustion of food in the organism. 2- Propellant production produces water as part of the Sabatier process output. For every methane molecule produced, four water molecules are required, and two water molecules are returned. 4H2O+CO2=2H2O+O2+CH4.
As production increases in a growing settlement, water may become an output from the fabrication of steel if a hydrogen reduction system is used.
Used water goes to the waste water treatment plant. It is purified using different treatments and the minerals and contaminants removed are recycled. The water is stored, or mixed with water from the settlement systems and returned to water treatment plant for reuse.