Chlorine is used for bacteria control as the others were saying, they do a spike in the early morning (typically) so you'll see higher levels at different times (normal ~.4ppm, batch ~.8ppm). It's safe to drink but not tasty, you can boil the water or let it sit to degas over time. A carbon filter is the most effective means but not an option if you live in an apartment. Chlorine hates copper, so you'll see accelerated wear if you don't use a carbon filter or replace the pipes with PVC composite.