Water profile

Kumenoyu

Spring chemistry and what it does, with the research behind it.

東道後第6・第8源泉Higashi-Dogo Springs No. 6 and No. 8

湯SimpleSodium Bicarbonate-Chloride spring

An alkaline simple thermal spring drawn from the Higashi-Dogo No. 6 and No. 8 wells, posted as feeding the main bath, hinoki bath, bubble bath, hand-and-foot bath, open-air bath and hot shower taps. Lightly mineralized and gentle in character, it carries the slippery, skin-softening feel of Japan's beauty-water family. Beyond the standard list of chronic muscle and joint complaints, the posted indications single out autonomic nervous system instability, insomnia and depressed mood — the calm-the-nerves profile typical of alkaline simple springs. Bath-side, the water is reheated to bathing temperature, run through recirculating filtration and disinfected with a chlorine-based agent to meet Matsuyama City bathhouse standards.

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

On the certificate:Muscle stiffness associated with motor paralysis

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

Recovery

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

fatigue, stress

On the certificate:Autonomic nervous system instabilityConvalescenceFatigue recoveryGeneral health improvementInsomniaDepressed mood

Take care

Contraindications

Active stage of any illness (especially with fever)
Active tuberculosis
Advanced malignant tumor or severe anemia with marked physical debilitation
Severe heart or lung disease causing breathlessness on slight exertion
Severe kidney disease with edema
Gastrointestinal bleeding
Visible bleeding
Acute exacerbation of a chronic illness

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%)

Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺168mgP42 national98%
CalciumCa²⁺1.3mgP4 national0.8%
LithiumLi⁺0.30mgP42 national0.5%
PotassiumK⁺0.90mgP11 national0.3%
StrontiumSr²⁺0.09mgP15 national
Aluminumshows up in acidic volcanic waterAl³⁺< —mg
BariumBa²⁺< —mg
Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
Iron (III)Fe³⁺< —mg
Magnesiummild; a laxative if you drink itMg²⁺< —mg
Manganesetrace; companion to iron springsMn²⁺< —mg
AmmoniumNH₄⁺< —mg
ZincZn²⁺< —mg

Anionsshare of charge (mval%)

Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻206mgP58 national46%
Chloridetable-salt anion — coats the skin and holds heat inCl⁻102mgP40 national39%
Fluoridetrace; drinking limits applyF⁻8.5mgP88 national6%
Carbonatestrongly alkaline; slippery feelCO₃²⁻13.3mgP58 national6%
Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻5.4mgP16 national2%
NitrateNO₃⁻0.50mgP60 national0.1%
HydroxideOH⁻0.10mgP49 national0.1%
BromideBr⁻0.20mgP29 national0.0%
Iodideyellows in air; helps blood lipidsI⁻< —mg
Thiosulfateoxidized sulfurS₂O₃²⁻< —mg

Non-dissociatedmeasured by mass

Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃45.7mgP25 national
Metaboric acidmetaboric acid — mildly antibacterialHBO₂14.3mgP67 national

Dissolved gasesmeasured by mass

Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.40mgP14 national
Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg

Trace metalsmeasured by mass

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

Measured at the source

Source temperature

42.2°C

Hot

Tonicity

0.57g/kg

Hypotonic

Free CO₂

0.40mg/kg

Low

On the certificate

Chronic muscle or joint pain and stiffness (rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains — chronic phase)
Cold sensitivity
Peripheral circulation disorders
Reduced gastrointestinal function (heaviness, bloating)
Mild hypertension
Impaired glucose tolerance (diabetes)
Mild hypercholesterolemia
Mild asthma or emphysema
Hemorrhoid pain
Stress-related symptoms (sleep disorders, depressed mood)

Evidence

東道後第2源泉Higashi-Dogo Spring No. 2

湯SimpleSodium-Calcium Bicarbonate spring

A weakly alkaline simple thermal spring from Higashi-Dogo well No. 2, the facility's second source. Lightly mineralized and soft on the skin, it is posted as feeding the cold plunge bath and the cold-water shower taps — even the cold bath here runs on spring water. According to the disclosure it is served without dilution or reheating, via recirculating filtration with chlorine-based disinfection. The posted indications span the standard range, from chronic joint and muscle pain and cold sensitivity to insomnia and depressed mood.