Make funnels collect water automatically.

With this change, to collect rainwater, you activate a funnel and then drop a water-tight, sealable container onto its tile. Then you wait. The funnel will try to add rain water to a container on its tile. (If multiple containers are present, it uses the largest one which is (1) water-tight and sealable and (2) doesn't contain a liquid other than water or acid.)

Dropping multiple containers on a tile won't help you, because the funnel won't switch automatically.

If a funnel is exposed to rain as well as acid rain before the container is collected, the liquid in the container may change to "weak acid water". This means you should try to pick up a water container very soon after it becomes full. (If water is exposed to acid rain and doesn't turn into weak acid water, it may become more poisoned instead, but boiling takes care of that.)

A funnel should collect around 14 charges of water per hour when it's raining, or 7 or so charges per hour during a drizzle. A makeshift funnel is easy to craft but is much smaller than a regular funnel and only collects 1% as much water.