Depending on where in the LA metropolis you live in, you might get your water from one of the aqueducts that receive their supply (eventually) from snowpack melt up in the northern mountains. When it snows. Which it hasn't much this year.
Some get theirs from the LA Aqueduct, and others – like the Las Virgenes Municipal Water District (which covers the cities of the West Valley and the largely unincorporated mountainous area west of LA) – get it from the California Aqueduct.
But since none of the houses or businesses have long straws to dip directly into their respective aqueducts or reservoirs, the water has to be delivered to them somehow.
The LVMWD not only provides the water itself, but a whole water service, including pumps, valves, 2500 fire hydrants, and maintenance of all of the above. Also, by state law, they have to restrict urban water use by 20% by 2020, which means cutting down on irrigation, sprinklers, lawn watering, leaks, etc.
The water delivered to those in the LVMWD comes from the area's regional water wholesaler, Metropolitan Water District, and travels east to west through a reversible pumping system, which can switch the direction from west to east in times of maintenance or other issues.
The LV #2 Connection, built in 1992 in Calabasas, is where the LVMWD facilities begin...
...and features a total of three pumps, only two of which run at any given time.
The water is pumped at a force equivalent to 600 horsepower, which is necessary because of the mountainous nature of the area, whose residents at high elevations can't receive gravity-fed water (like from the LA Reservoir).
This serves the 122 square mile service area of the water district, which has no native supply of water, making it essential to import it all.
In an underground chamber, you can find the pressure valves...
...and the large pipes that can deliver the water in either direction (west or east).
There are nearly 300 miles of pipes to move water around the entire district.
At the Cornell Pump Station, there's a big diesel engine that's like a big car with a V8 engine...
...that powers a catalytic converter-type filtration system...
...along with an electric pump...
...which is employed before the gas pumps.
This is where they can switch the direction of the water flow, from east/west to west/east.
Depending on the water demand at the time, the supply is either pumped directly into homes...
...or to the Las Virgenes Reservoir in Westlake Village.
Built between 1970-1972, at 120 feet deep at full capacity (with 20 feet of unusable deadwater at the bottom), it holds a big enough water reserve that could supply water for six months in an emergency, which is about three billion gallons.
The water is contained by two earthen dams including the Saddle Dam and the dam at Three Springs Park.
Unlike the LA Reservoir, this reservoir is uncovered, but also protected under tight security: fenced off from land-walking wildlife (although birds can get in), human contact is prohibited, which means no recreation at this nice-looking lake.
Along the Saddle Dam is the Westlake Filtration Plant...
...which filters and disinfects (again) any water drawn from the Las Virgenes Reservoir.
Built in 1989 and in operation mostly during the summer (when water is needed most)...
...it's capable of processing up to 15MM gallons of water per day.
First, the water from the reservoir comes in through the dam and is filtered through units that use diatomaceous earth (fossilized remains of hard-shelled algae that is baked and ground up into a fine white powder) as filtration media. DE has other common household uses as an absorbent, insulator, filler, and abrasive – and is even available in food grade (e.g. for use as an insecticide).
After filtration, the water goes through disinfection using chloramines (just like at the LA Reservoir filtration plant), and then out to thirsty residents.
Incidentally, the Las Virgenes Reservoir and filtration plant were the last place that Huell Howser visited before his death, and were the last location featured in his California Water series (starts around the 18 minute mark).
Photo Essay: Keeping LA's Water Supply Drinkable (and Accessible)
Photo Essay: The Power Plants of the St. Francis Dam Disaster