What did people do before (something)?

Sometimes it's hard to imagine how people lived in the past without the conveniences that we have today, like refridgerators, showers, computers, and cars. 

To talk about this feeling, use the expression "What did people do before...?" For example:

What did people do before they had cell phones? It must have been so hard to get in touch with people.

What did people do all the time before television?

back (in a time period)

Use "back" to talk about a time period in the past:

Back in the '80s, there was graffiti all over the place in the city.

Back when I was in school, teachers would spank you with a paddlie if you misbehaved.

The time period is usually more than a year ago. It would be strange to use this to talk about something that happened yesterday or last week.

Adding this word makes the time period seem like it was a long time ago.

(people) have running water

"Running water" is water that's moving. The alternative is "standing water". A river, a stream, and a faucet all have "running water". A pond, a lake, and a well all have "standing water". Water in an ocean wouldn't really be considered either "running" or "standing".

When people have working faucets in their homes, you can say that they "have running water".

(Who/What/Why/etc.) do you think (question)?

You can ask people "What do you think...?" to get their opinions on something:

What do you think this sentence means?

But people also ask "What do you think...?" to kind of make fun of a person for not knowing something, or to get angry at someone for asking a dumb question:

A: What are you doing?

B: What do you think I'm doing? I'm cooking dinner! 

The same applies for other question words: "Why", "When", etc.:

A: Hello? Who's this?

B: Who do you think it is? It's me!