sensitu ga tigau.

が marks 泉質 as the thing that is different.

With 違う, the thing that differs is often marked by が:

• 味が違う = The taste is different.
• 色が違う = The color is different.
• 泉質が違う = The spring quality/composition is different.

If you used は instead, the nuance would change. は would make 泉質 the topic, often with a contrastive feeling:

• 泉質は違う。 = As for the spring quality, it’s different.

So が is the most neutral way to say that the spring quality itself is different.

Even though English uses the adjective different, Japanese uses 違う, which is a verb.

That is why it conjugates like a verb:

• dictionary form: 違う
• polite form: 違います
• past: 違った
• negative: 違わない

So 泉質が違う is grammatically more like The spring quality differs than The spring quality is different, even though the natural English translation may use different.

泉質 usually refers to the quality, type, or mineral composition of hot spring water.

It is a common word in the context of onsen. It does not just mean ordinary water quality in a general sense. It often refers to what kind of hot spring water it is, such as:

• sulfurous
• alkaline
• acidic
• rich in certain minerals

So in an onsen context, 泉質が違う often means something like:

• The mineral composition is different.
• The type of spring water is different.

That is very normal in Japanese. The comparison target is often omitted when it is clear from context.

So 泉質が違う could mean:

• The spring quality is different from this other bath.
• The spring quality is different from one hot spring to another.
• This place has different spring water than the previous one.

Japanese often leaves out information that the listener can infer. In English, you may feel that something is missing, but in Japanese this is very natural.

Yes. 違う is often seen in the pattern:

• AはBと違う。 = A is different from B.

But it can also be used without stating the comparison explicitly, when the other thing is understood from context:

• 泉質が違う。 = The spring quality is different.

So と is not required if the sentence does not need to say what it is different from.

Yes, it would be correct, but the nuance is different.

• 泉質が違う。
  Neutral statement: The spring quality is different.

• 泉質は違う。
  Topic/contrast nuance: At least the spring quality is different or As for the spring quality, that part is different.

Using は often suggests contrast with something else, whether stated or unstated. For example:

• 場所は同じだけど、泉質は違う。
  The place is the same, but the spring quality is different.

The plain form 違う is the basic dictionary form and is commonly used in:

• casual speech
• written descriptions
• headlines
• notes
• explanatory text

The polite version would be:

• 泉質が違います。

Both are correct. The choice depends on the level of formality.

Yes, but in Japanese the plain non-past form 違う covers both:

• present meaning
• general truth
• sometimes future meaning, depending on context

Here it most naturally means a present or general statement:

• The spring quality is different.
• The spring quality differs.

It is not limited to a strict English-style present tense.

It is read:

せんしつ が ちがう

Breakdown:

• 泉質 = せんしつ
• が = が
• 違う = ちがう

A native English speaker may want to be careful with ちがう, since the ち sound is like chi, not ti.

Japanese nouns usually do not mark singular vs. plural.

So 泉質 can refer to:

• the spring quality of one hot spring
• the spring quality of different springs in a general discussion

The exact meaning depends on context. Japanese does not need articles like a or the, and it usually does not need plural marking either.

Possibly, yes. Japanese often omits the topic if it is already known.

For example, the full context might really be something like:

• この温泉は、泉質が違う。
  This hot spring has different water quality.
• こことあそこは、泉質が違う。
  The spring quality here and there is different.

When you see a short sentence like 泉質が違う, it often appears in a context where the speaker has already established what they are talking about.

Yes. Both are reasonable.

• 泉質が違う = The spring quality is different.
• 泉質が違う = The spring quality differs.

In English, is different is often more natural in everyday speech, while differs is a bit more compact or formal. The Japanese sentence itself does not force one specific English wording.

Yes. 水質 means water quality in a broader sense and can be used for drinking water, rivers, pools, and so on.

泉質 is specifically about the nature or composition of a spring, especially hot spring water.

So in an onsen context, 泉質 is the more natural word. It sounds much more specific than 水質.