Less than you'd think — and it depends on you. People assume a deeper bath must mean a lot more water. It doesn't. How much you actually run comes down to how high you fill it and who's getting in — and a deep Omnitub soak uses about the same water as an everyday bath, for a far deeper, hotter one. Share it, and it's even less per person.
You fill to the soak line, not the brim
Our deep soaking baths have a 600mm internal depth — but that's headroom, not a fill target. In normal use you fill to the 525mm overflow: the soak line almost everyone uses. You can fill closer to 600mm if you really want, though there's little room to move at that point. The extra depth isn't water you have to heat — it's there so the water sits comfortably above your shoulders. (Our seated and plunge tubs are deeper again, with their own soak lines — more below.)
More bodies, less water
Here's the part most people forget: when you get in, your body displaces water — roughly its own weight in litres. And because most Omnitubs are built for two or more, that adds up. Two people sharing one deep soak displace far more water than one — so you run less, and you're filling a single shared tub instead of running two separate baths. The more of you in it, the less water each, for the same deep soak.
So, how much?
For a single bather in our smallest tub, filled to the soak line, you're looking at roughly 175–200 litres depending on weight — about the same as a typical family bath. Share a two-person tub and the water per person drops further. It's all relative to you, which is why we don't quote one “capacity” number — our free OmniSoak calculator works out your exact litres from your tub, fill depth and each bather's weight.
Hot or cold? Hitting your perfect temperature
OmniSoak also splits the fill into hot and cold. To reach a 40°C soak by mixing 60°C hot with 10°C cold mains you need roughly 60% hot to 40% cold — but the real split depends on your hot-water tank and incoming mains, which is why the tool does it for your setup.
Want to go deeper still?
Our Japanese seated tubs take it further — 1000mm of depth to sit upright, immersed to the shoulders, in a compact footprint. Same principle: fill to the line, your body provides some of the volume, and OmniSoak gives the exact figure.
→ Work out your exact fill with OmniSoak · Explore deep soaking baths · Japanese seated tubs