Water profile — Nanadaru Onsen Hotel

七滝温泉ホテル源泉Nanadaru Onsen Hotel Spring

硫Sulfate

A calcium-sodium sulfate spring rising at Nashimoto in Kawazu. Calcium and the sulfate ion carry almost the whole of the mineral load, and at 1,012 mg/kg of dissolved solids the water has noticeable body without feeling heavy. The posted summary files it as hypotonic, alkaline and high-temperature, with iron and magnesium present only in traces — a settled, quietly mineral-rich sulfate water rather than a sharp or strongly scented one.

Good for

Aches & joints

Warmth eases stiffness and raises the pain threshold. Radon and sulfate springs show the strongest evidence for joint and muscle pain.

stiff shoulders

Circulation

Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.

tired legs

Smooth skin

Bicarbonate and alkalinity gently lift dead keratin while silica hydrates, leaving skin smooth. This is the basis of the beautifying-water (bijin-no-yu 美人の湯) reputation.

dry, rough skin

Cuts

Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.

minor wounds

Recovery

Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.

fatigue, stress

Full composition

The bar is each ion's share of charge (mval%) within its group; over 20% names the spring. Gases, silica and trace metals are measured by mass only.

Cationsshare of charge (mval%)

Calciumsettling and calming; can leave a white mineral bloomCa²⁺169mgP84 national
Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺167mgP43 national
Potassiumminor; matters for drinking limitsK⁺4.4mgP33 national
StrontiumSr²⁺0.40mgP61 national
Iron (III)Fe³⁺0.10mgP58 national
Magnesiummild; a laxative if you drink itMg²⁺0.10mgP11 national

Anionsshare of charge (mval%)

Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻576mgP89 national
Chloridetable-salt anion — coats the skin and holds heat inCl⁻49.9mgP26 national
Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻20.5mgP13 national
Carbonatestrongly alkaline; slippery feelCO₃²⁻1.0mgP17 national
Fluoridetrace; drinking limits applyF⁻0.40mgP28 national
Bromidetrace, sea-originBr⁻0.20mgP28 national

Non-dissociatedmeasured by mass

Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃22.7mgP7 national
Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.30mgP7 national
Metaarsenious acidHAsO₂0.01mgP30 national

Dissolved gasesmeasured by mass

Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂4.4mgP28 national

Trace metalsmeasured by mass

CadmiumCd< —mg
CopperCu< —mg
Mercurytoxic trace — part of the drinking-safety checkHg< —mg
LeadPb< —mg

Measured at the source

Source temperature

54.2°C

Hot

Tonicity

1.01g/kg

Hypotonic

Free CO₂

4.40mg/kg

Low

Evidence

菊水天城源泉Kikusui Amagi Spring

湯SimpleCalcium-Sodium Sulfate spring

Kikusui Amagi Spring rises at Tanaochi in Nashimoto, Kawazu, and is classified as an alkaline simple thermal water (hypotonic, alkaline, high-temperature). At 965 mg/kg of dissolved solids it is lightly mineralized and gentle on the body, while pH 8.5 gives it the slippery feel that puts it squarely in Japan's beauty-water family. It also carries 52 mg/kg of metasilicic acid — enough to leave the thin silica film that makes skin feel noticeably smoother afterwards — and comes out of the ground almost colorless, clear, tasteless and odorless. A poster at the inn describes a lava-cave bath run free-flow from the source, bathed mixed in swimsuits and open to overnight guests free of charge from 9:00 to 18:00.