yòng pēnhú jiāoshuǐ.

Chinese often uses the pattern 用 + tool/instrument + verb to mean use X to do Y.

So:

• 用 = use
• 喷壶 = watering can / sprayer
• 浇水 = water; pour water on

So 用喷壶浇水 literally means use a watering can to water.

This is different from English, where the tool often comes later: water with a watering can.

Yes, it can be a complete sentence in context.

Chinese often leaves out the subject when it is obvious. Depending on the situation, the hidden subject could be:

• you — in an instruction
• someone — in a description
• I / he / she / they — if already understood from context

So this could mean things like:

• Use a watering can to water.
• (He/She) uses a watering can to water.

If you want to state the subject clearly, you can say:

• 我用喷壶浇水。 = I use a watering can to water.
• 他用喷壶浇水。 = He uses a watering can to water.

喷壶 literally means something like spraying pot/container. In real usage, it can refer to a sprayer, spray bottle, or a plant-watering container, depending on context.

In this sentence, because the action is 浇水, learners usually understand it as a watering can or similar tool used for watering plants.

If you want to be extra clear about watering can, 浇水壶 is also common.

浇水 literally means to pour water on something.

Very often, in everyday Chinese, it means to water plants. But it can also be used more generally for pouring water onto something.

Examples:

• 给花浇水 = water the flowers
• 给植物浇水 = water the plants

So in this sentence, 浇水 most naturally means watering plants.

Chinese often leaves out the object when it is obvious from context.

In a gardening context, people will naturally understand that you mean something like:

• the flowers
• the plants
• the garden

So 用喷壶浇水 does not need to say exactly what is being watered if that is already clear.

If you want to include the object, you could say:

• 用喷壶给花浇水。 = Use a watering can to water the flowers.
• 用喷壶浇花。 = Use a watering can to water the flowers.

Because the sentence is talking about the tool in a general way, not counting it.

After 用, it is very normal to put a bare noun:

• 用喷壶浇水
• 用筷子吃饭
• 用手机拍照

You only need a number or demonstrative if you want to be specific:

• 用一个喷壶浇水 = use one watering can to water
• 用这个喷壶浇水 = use this watering can to water

So the original sentence is completely natural.

Yes. 用喷壶来浇水 is grammatical and natural.

The 来 here helps mark purpose, something like use a watering can in order to water. But in many everyday sentences, 来 is optional.

So:

• 用喷壶浇水
• 用喷壶来浇水

Both work. The version without 来 is shorter and very common.

You can, but the nuance is a little different.

• 用喷壶浇水 focuses on the instrument: use a watering can
• 拿喷壶浇水 focuses more on taking/holding the watering can and then watering

So if you want the most neutral way to talk about what tool is used, 用 is better.

By itself, it can work in more than one way depending on context.

It might be:

• an instruction: Use a watering can to water
• a description: (Someone) uses a watering can to water
• an action label/caption in a textbook or picture

If you want to make it clearly a command, you can say:

• 请用喷壶浇水。 = Please use a watering can to water.
• 用喷壶浇水吧。 = Use a watering can to water.

It is pronounced:

用喷壶浇水
yòng pēnhú jiāoshuǐ

Tones:

• 用 yòng — 4th tone
• 喷 pēn — 1st tone
• 壶 hú — 2nd tone
• 浇 jiāo — 1st tone
• 水 shuǐ — 3rd tone

There are no unusual tone changes here.