Does the Hewelth UVClean self-cleaning mode work if the bottle is only half full?

I only fill mine about halfway most days and the self-cleaning mode has been fine for me. I’ve had it a couple months and no weird smell or film buildup, so it doesn’t seem like it needs a full bottle to do its thing.

My sister has this bottle and she almost never fills it past the middle. She’s been using it that way since around the holidays and hasn’t had any issues with smell or slime, so from what I’ve seen it does its thing with less water in there. I borrowed it for a weekend trip once and did the same thing, just partial fills, and it was fine. I don’t think the light cares much about the water level as long as it’s hitting the surfaces inside. If anything I’d guess more water might actually block the light from reaching the upper parts, but that’s just me thinking out loud. She did notice once that when she left it sitting with just a tiny splash at the bottom for like two days, it started smelling a little off, but she refilled it and ran a cycle and it cleared up. So my take is half full is totally fine, just don’t leave it nearly empty for long stretches. That seems to be the only time it struggles. Not sure if that’s the UV or just normal bottle gunk though.

UV light doesn’t care about water level, it just hits surfaces. But if it’s half full, the light’s gotta reach the entire inside including the upper walls. Mine still smelled fine after a week of half fills, so who knows.

I’ve gotten into the habit of topping mine up before bed even if it’s not full, just because that’s when the six hour cycles seem to line up best for me. I still run it at whatever level though. The only thing I’ve really noticed is that a fuller bottle just feels colder longer, which has nothing to do with the cleaning part.

The half full thing is backwards for me. I had one of these and the cleaning was noticeably weaker when the bottle was low. Not because the light needs water depth, but because with less water the light reflects differently in there. When mine was near empty the inside still smelled a bit off after a few days. When it was mostly full, no issue. I tested this over about three weeks with the same bottle and same routine. Filled it halfway for a week, then full for the rest. The full stretches were the only ones where the odor stayed gone. So I don’t buy the idea that water level doesn’t matter. Maybe the lamp is just weak, but that was my experience. I ended up returning mine anyway because the cap started acting up after a month. Point is, half full wasn’t cutting it for me.

Half full is exactly when I notice the smell coming back sooner. Mine does fine when it’s topped up, but leave it low for a day and the inside starts getting that stale thing going. So no, I don’t buy that the level doesn’t matter.