How to deal with rat droppings near water heater?

[Bruce P.]

Hi, 

So my friend Jenny recently bought a SFH in the LA area. When a contractor was in the attic one day, he mentioned to my friend Jenny that he saw a rat. So Jenny bought some glue traps and put them up in the attic and went about her life.

Recently this month, Jenny discovered what appeared to be a bunch of rat droppings near the water heater (see attached photo). The water heater is in a closet in the hallway. After checking the glue traps, she realized no rats had been caught.

1) How did the rats get from the attic to the water heater?

2) What's the next step to try and remedy this situation? Try different rat traps in the attic? Put rat traps in the water heater closet?

There were a few times at night Jenny thought she heard some shuffling coming (possibly) from the attic at night, but she hasn't heard them in a while. 

Thanks in advance!