Very nice. I have a PrC called the elemental conjurer (imagine that!) and these would go very well with it. They get the ability to create an elemental construct at 8th level, but it's only one size. (It's posted here:
http://www.geocities.com/mistmane/3E/prc/econjurer.html) These would go well with a Summon Elemental spell, though...
Just a few things: Why do water constructs have electrical attacks instead of ice attacks? I can't imagine any reason for them to have electricity. And how come they don't have the Engulf ability like Fire constructs? This would be perfect for a water construct - run over someone, engulf him, and drown him.
Natural attacks don't deal *1.5 Str, unless I'm mistaken; only weapons used with both hands deal the extra damage.
How come earth elementals don't have acid resistance 5? Acid is generally considered an Earth attack, since no one's really come up with earth spells.
I think there needs to be a cap set on ability usage. Having a fire elemental, for example, make things burst into flame at will as a free action is way too powerful. Three times a day is fine.
All the abilities should have Ex, Su, or Sp after them, BTW, since some abilities provoke AoOs.
Why is the water construct's good save Fort? I would think it would be Ref.
Are these are constructs in the literal sense of the word (as in creature type) or normal elementals? If the former, they wouldn't have Con scores, and their Int scores would liikely be a lot lower.
- Stomp: At will as a standard action, summon may stomp the ground. All creatures within 10 ft. who are on the ground not immune to Tremor damage must make a Reflex save [DC 10 + 1/2 HD + Str bonus] or take 1d4 subdual damage and fall prone.
There is no tremor damage. Any creature on the ground must make this save.
- Great Strength: Summon gains +18 Enhancement bonus to Strength.
Whoa. That's a bit much, don't you think? They already get huge bonuses to hp... you give them this, too, and he'd be a bit overpowered.
- Tremor: At will as a standard action, summon may cause the ground to shake (Medium range). All creatures in a 10 ft. burst, who are on the ground and not immune to Tremor damage, must make a Reflex save [DC 10 + 1/2 HD + Str bonus] or take 1d4 subdual damage and fall prone.
"Medium range" needs to be clarified (i.e., 400 ft. + 40 ft./level; set a caster level for this). The first time I read it, I was wondering why it was on the same level as Great Stomp, which is clearly better.
All in all, though, I like this. I'm going to yoink it for the E-Conjurer.