When there's rain, line your containers underneath the points of heaviest rainfall to collect water. Since my balcony has a cover, the rain falls mostly near the railing.



Wait for your container to fill up, then cover tightly with lid. You need to cover the water because still water is a breeding ground for mosquitoes. This page will explain much better than I can.



And as for algae growing in the clear plastic containers, I've been using this rain water collection for the past month and have not encountered any problems. Since my collection is at such a small quantity, I use the water relatively quickly. Also, my northern-facing balcony gets little sun, and the water is kept in the corner, so this is probably why algae doesn't pose a problem for me.



If your balcony has no sunshade covering, or receives a lot of sun, you might have to either use dark colored containers, or keep them stored under a tarp, in a storage box, or even inside your apartment.



*Note: I also lined my plastic watering can under the sunshade to collect rain water. It's great because it can hold more water, but you do need to find something to cover the opening once it's filled. Or, if you're going to able to use all the water up right away, then go ahead and leave it uncovered. Either way, I'd suggest you try to use the water from the watering can before you use the container-stored water.

