Do You Know the Difference Between Groundwater and Surface Water?

San Jose Water (SJW) delivers water from three major sources: groundwater, imported surface water and local mountain surface water. Each water source has its own distinct quality and therefore goes through unique processes so that it meets or surpasses all state and federal drinking water regulations.

Groundwater

SJW’s groundwater is pumped from more than 100 wells that draw water from the Santa Clara groundwater basin. Groundwater, which makes up 38% of SJW’s supply, differs from surface water in key ways.

While groundwater generally has a higher mineral content than surface water, it requires less treatment than surface water. To help ensure that customers only receive safe, high quality water, chlorine is added to groundwater to prevent growth of bacteria in the pipes and tanks of the water distribution system.

Below a certain depth, the ground, if it’s permeable enough to hold water, is often saturated with water. The upper surface of that wet zone is known as “the water table.” Below that is what’s called an aquifer. Aquifers, layers of water-bearing rock, sand or gravel, act as huge storehouses, or reservoirs, of water. Groundwater is accessed by drilling wells into aquifers and pumping water out. Nationally, groundwater only accounts for 20% of water used. The largest reservoir in Santa Clara County is our groundwater aquifer. 

Imported surface water

While groundwater comes from aquifers via wells, surface water comes from mountains, lakes and rivers. SJW purchases imported surface treated water from the Santa Clara Valley Water District (SCVWD), accounting for 55% of its supply. The SCVWD provides water from the Sacramento-San Joaquin Delta, much of which originates as Sierra snowmelt, travels through state and federal water projects, and is then treated at SCVWD’s three water treatment plants.

Like surface water sold by all water providers, SJW’s imported surface water is filtered and disinfected with  chloramines at water treatment plants in order to make it safe for drinking.

Local mountain surface water

Locally sourced surface water, which accounts for 7% of SJW's water supply, goes through similar disinfection procedures at SJW’s two water treatment plants. SJW receives its local surface water via local rainfall in its watershed in the nearby Santa Cruz Mountains.

What type of water are you, specifically, receiving?

To find out more about the type of water delivered to your home, you can consult the SJW Service Area and Water Supply Sources map, which indicates the predominant source in your area. For more specific information about your source of supply, you can call SJW at (408) 279-7900.