Mixed Conditionals: a mistake or correct?
Dear native speakers of English, I have a question to you. In one of the famous coursebooks of the Upper-Intermediate level I have found this task:

Make conditional sentences based on the information in these situations.

1. I don't use the dishwasher much, because no one told me that you use more water washing dishes by hand.

I would answer like this:

If someone had told me that washing dishes by hand uses more water, I would use the the dishwasher more (the Past Simple is used in the last part because it is related to the present life and from time to time I use it).

But The Techer's Book gives the answer like this:

If someone had told me that washing dishes by hand uses more water, I would have used the the dishwasher more.

The question is why we use would + the Perfect infinitive in the last part? The situation is about the present, not about what could have happened in the past.

Look forward to your ideas impatiently!One more situation:
We bought a cheap dishwasher that wasn't very efficient. As a result, we use a lot more water than we need to.
The answer:
"If we hadn't bought such a cheap dishwasher, we would use much less water. "
But they already use more water. Following this logic, we should say "we would have used less water".
What about this situation? Why do they use Conditional 2 in the answer in the last part?

Question

Mixed Conditionals: a mistake or correct?
Dear native speakers of English, I have a question to you. In one of the famous coursebooks of the Upper-Intermediate level I have found this task:

Make conditional sentences based on the information in these situations.

1. I don't use the dishwasher much, because no one told me that you use more water washing dishes by hand.

I would answer like this:

If someone had told me that washing dishes by hand uses more water, I would use the the dishwasher more (the Past Simple is used in the last part because it is related to the present life and from time to time I use it).

But The Techer's Book gives the answer like this:

If someone had told me that washing dishes by hand uses more water, I would have used the the dishwasher more.

The question is why we use would + the Perfect infinitive in the last part? The situation is about the present, not about what could have happened in the past.

Look forward to your ideas impatiently!One more situation:
We bought a cheap dishwasher that wasn't very efficient. As a result, we use a lot more water than we need to. 
The answer:
"If we hadn't bought such a cheap dishwasher, we would use much less water. "
But they already use more water. Following this logic, we should say "we would have used less water".
What about this situation? Why do they use Conditional 2 in the answer in the last part?

Answer

Hi, the ‘had...would have’ construction is in the past, as Wahid said. If someone had told me this, in the past, then I would have done...whatever it is. It’s about what has happened up until now, i.e if you had known  the facts, then you would have, up until this point, acted differently.
The way the question you quote is phrased makes it a bit unclear, as the question uses the present tense, what the person is doing or not doing now, implying that although they now know they still haven’t changed what they do. In changing this into the conditional with ‘had...would have’, you automatically move this into the past.

Answer

The reason you would used the past form of the conditional is because the "condition" was described or defined in the past:

"If someone HAD told me that washing dishes by hand uses more water, I would have used the dishwasher more."

By adding the auxillary verb "had," the speaker is defining a "condition" which previously existed.

You could make it clearer by stating the time for example:  "LAST WEEK, if someone HAD told me...."  So, the conditional response must also be set in the past... "I would HAVE...."

If the condition were set in the present, you would used the present form of the conditional: "If someone told me.... I would..."

Answer

If someone had told me that washing dishes by hand uses more water, I would have used the dishwasher more. 
(This is a type 3 conditional.) The type 3 conditional is used to refer to a time that is in the PAST, and a situation that is CONTRARY TO REALITY.

If someone had told me that washing dishes by hand uses more water (If this thing happened in the PAST),

I would have used the dishwasher more (this kind of "reality" could have happened. HOWEVER it is NOT happening in REALITY at the moment. It is the CONTRARY. She is possibly still washing by hand alot instead of using a dishwasher more.)

Type 3 conditional structure:
If + past perfect (had + past participle)	---------- perfect conditional (would + has/have + past participle)
If this thing had happened	----------------------------------------------------that thing would have happened (but it didn't happen)
If someone had told me that washing dishes by hand uses more water,------------ I would have used the dishwasher more. (meaning she didn't use the dishwasher more)

source of my explanation:
https://www.ef.com/english-resources/english-grammar/conditional/

Answer

You would say "I would have used the dishwasher" because you are describing a conditional, hypothetical situation in the past, not the present. You would have done your dishwashing with a dishwasher in the past, not at the present moment.