According to Reformed theology, is teaching a false Trinitarian concept considered blasphemy? There are several people that do not understand the trinity. I hear things such as "God is like water. He is liquid, steam, and solid". This analogy actually comes with a longer explanation about how the holy spirit guy is steam and god the son is solid. However, this is modalism, showing three distinct "modes" or "functions" of the triune god.

I also hear the triune god is like an egg. He is shell, white, and yolk, but one egg. Some even go as far as to say each person is "one-third god". This is actually a form of tritheism, in that each person of the triune god is a "part" of the triune god, thus separating the "divine nature".

Some people are confused about the hypostatic union, and they separate the divine and human nature of the second person of the triune god, god the son. Thus, "they deny that Jesus came in flesh", which 1 John 4:3 says "is the spirit of the antichrist".

According to Reformed theology, are the people who share and promote these misunderstandings spreading blasphemous lies?
These are only limited or weak examples of analogy for Trinity. They are not called as heresy by scholars. Trinity is accepted as mystery by vast majority when it comes to rational explanation. We too must not stretch the emphasis on rational explanation as to condemn the imperfect analogies as heresies. The 3 forms of H2O analogy may be misunderstood as Modalism but it can also be taken as same divine nature of the three persons. It does not necessarily imply Modalism.  

We should admit that an analogy is only an analogy which only expresses a limited resembles of the doctrine ; and all analogies would come short of completely describing it perfectly.