The speaker has a single 50mm driver and passive bass radiator and sounds decent for a very compact speaker. It doesn't have as much bass as the larger BoomBottle, but it has a reasonable amount of clarity so long as you don't push it too hard with bass-heavy or complicated music.
Most people will end up leaving it resting upright on a table or flat surface and if you stick it in a corner or near a wall you'll get a little more bass. In case you want to hang it from somewhere, there's a loop on top and you'll find a carabiner clip in the box.
For those trying to decide between this model, and the bigger BoomBottle which has two 40mm drivers, the latter model sounds a little fuller and plays slightly louder, but it's not a night and day difference, so you don't feel like you're giving up too much in the performance department.
That said, you shouldn't expect this to produce meaty bass and it can come off sounding comparatively thin when feeding it hip-hop and techno tracks. For instance, I fed it Janelle Monae's "Q.U.E.E.N." and tried cranking the volume, and it sounded pretty rough.
The speaker charges via Micro-USB and is rated at 11 hours of battery life, which is slightly above average for these types of mini-Bluetooth speakers. If you play your music at more moderate volume levels, you may be able to exceed that number.
While this speaker doesn't offer the sound quality (or maximum sound output) of a more premium canister-style speaker like the UE Boom, it does cost significantly less and offers decent sound for its size, though it does have its limitations.
The BoomBottle H2O's list price is $100 (£100), but once it gets wider distribution, I expect you'll see it for less (the bigger BoomBottle, lists for $150 or £120, but can be had for around $105 or £90 online; the smaller BoomBottle Mini retails for $50 or £50).
The Divoom Voombox Travel (around $50, £50) and Voombox Outdoor (around $100, £100) are arguably slightly better values (at least at this moment), but the BoomBottle H2O is a recommendable speaker that's worth a hard look, particularly if you see it selling for less than list.