Save money for large volume filtering? Use a 20 litre solar shower bag as the unfiltered water resouvoir. If one of the gravity devices or screw straw can be fitted to it? Assuming the newer straw version can operate by gravity feed?

To me the two best options are the improved newer straw version with a screw thread. If common water bottles can be fitted to the screw? More useful than the simple straw requiring sucking. External to the bottle so easier to carry just the "straw". Use a disposable one litre bottle in the field to refill canteens etc.

The 3.7 L gravity filter or the 5 L version of the bigger filter, depending on price, $220 for thecway L is ridiculous compared to 3.7 L $90 bag. A gravity bag if light enough, to carry in a day pack. If larger volumes of water need filtering, not just emergency use.

In camp useful for filtering drinking and cooking water.

Last Top End buffalo trip a guest refused to drink from the running stream. I have previously used it for cleaning, cooking, and drinking water at need. An 160 I'm round trip drive to fill the water jerry cans. I stupidly had forget to fill them all when in town. Just one 20L as emergency highway water supplies. BTW the service station in Katherine where we always used to get town water now refuses to supply it. Though they let us fill up 2x 20L jerry cans. "Grey Wanderers" were regularly filling up 200 litre caravan water tanks and costing the servicecstation too much. Not sure where else to get it in Katherine?

A 3.7, 5, or 20 L gravity fed filter could filter a 20 L jerry can every two hours or so. Saves half a day and hundreds of kms water resupply!

Bore water is often a good remote drinking water source. Can be a bit saline sometimes.

I wonder how much these lifestraw products clean out salt from saline water?

Very useful products.