The projects will focus primarily on the oil-rich country's bulging biggest cities. Some $11 billion will be spent on more desalination plants, which convert sea water into fresh water, as natural supplies run out.
Some of these are expected to be powered by solar energy.
Saudi Arabia, which averages 4 inches of rain a year, is considered the largest producer of desalinated water in the world.
Desalination plants supply 116.6 million cubic feet a day, or 18 percent of the global total, through a supply network covering around 2,500 miles. They also supply 43 percent of the combined reservoir of the six-member Gulf Cooperation Council.
The GCC also includes the United Arab Emirates, Kuwait, Oman, Qatar and Bahrain.
Most of the spending will go on wastewater projects but the NWC says $30.66 billion will go on boosting the water supply in 2012-20.
One of the primary objectives is to staunch large-scale leakage from the water system.
That's a major problem across the Middle East where water supply has been shrinking because of antiquated water systems, aggravated in recent years by serious drought and global warming.
NWC says water saved from leakage in Riyadh and Jeddah has increased from 256.07 million cubic feet in 2008 to 2.3 billion cubic feet in 2011.
"This is a particularly important factor in Saudi Arabia, where water is expensive to produce," the Middle East Economic Digest observed.
Saudi Arabia's water supply has increased from 26.77 billion cubic feet in 2008 to 36.66 billion cubic feet in 2011.
MEED reported the Saudis are also driving to minimize the use of desalinated water for projects that don't require potable water.
"Saudi Arabia plans to use treated sewage effluent, or TSE, more effectively," the weekly noted.
"The NWC intends to create TSE businesses from its existing wastewater assets in developing a long-term market for treated wastewater.
"TSE is currently only used in Riyadh and Jeddah on a very small scale," MEED reported.
But TSE usage is expected to triple by 2030. TSE sales have gone from zero in 2008 to 17.48 million cubic feet this year.
"As a result, TSE is becoming an important revenue stream for the NWC," MEED said.
Revenue is expected to exceed that from potable water sales in Riyadh and five other major cities by 2022. By 2030, it's estimated that potable water sales will total $754.5 million.
The Saline Water Conversion Corp., which operates more than 30 desalination plants on the Persian Gulf and Red Sea coasts, disclosed recently it's implementing several new desalination projects at a total cost of $10.66 billion.
On Thursday, Water and Electricity Minister Abdullah Al-Hussayen said the kingdom intends to rely heavily on solar energy to operate desalination plants instead of using oil and gas.
Increasingly, the kingdom is using hydrocarbons for power generation, including the energy-intensive desalination plants that are the main source of water.
As more and more oil and natural gas is diverted to generate greater amounts of electricity as the demand for power swells amid industrialization and a burgeoning population, the amount available for export, Saudi Arabia's economic lifeblood, shrinks.
The International Energy Agency has estimated that Saudi Arabia's rate of direct crude burning more than doubled in 2008-10 because of the rapid increase in demand for electricity and a shortage of natural gas.
Just how much of that went to desalination isn't known but the experts believe it was significant.
Some authorities say that natural water supplies, such as underground aquifers, are being dangerously depleted or salinated as seawater replaces fresh water in these reservoirs.
Water use in the kingdom, which is largely desert, is almost double the per capita global average and is increasing at an even faster rate because of industrialization and population growth.
This has heightened the need for greater desalination projects. Hussayen warned in May that the nation's demand for water is increasing by more than 7 percent a year.
To counter this, the water and power sector needs $133 billion in investment over the next decade, he said.