VOA常速英语:喝到嘴里的水是如何被“洗”干净的

This water needs a good wash before it ever reaches your faucet.

Whether you are treating for a population of 3000 or for 3 million this process is going to look a lot like this.

It’s called conventional water treatment and it makes lake and river water safe to drink.It starts with a chemical that attracts and binds together the stuff you want to take out.

We add those coagulant and it’s positively charged while most of the dirt and bacteria are the negative charge.

It’s a crucial if temporarily backward step.

When we added our coagulant it actually made the water dirtier.We created these flocks but now as we are going, all those flocks are settling out.

This process sedimentation makes the things you don’t want to drink sink,a key step in creating cleaner water for you and for the rivers.

This is all part of the process that diverts those salads should be returned to the river and put beneficial usage instead.

In this case the solids will coat a landfill. Now back to the drinking water.

There are some small fine particles that can float on that aren’t removed by gravity settling and here is where we remove those small particles.

The technical name is dual media filtration which means that within any one filter,water flows through both coal and sand in case you wonder how they clean those filters: backwash.

In the next step, filtered water is disinfected by adding chlorine.Each step is lab-tested something important in times of erratic weather.

If you’ve got a lot of rain in the watershed it can stir up dirt and debris and carry that into the river.When that’s taken into a water treatment plant,you need to increase your coagulant dose to account for that higher amount of solids in the river.

Engineers at this cutting edge treatment plants say modern technology can keep today’s drinking water cleaner and safer than any other point in history.

Arash Arabasadi, VOA News, Washington.