The Archer's jet should be acid instead of water

Squirting arcing water doesn't look convincing. Acid would be more efficient at suspending disbelief.

Water could still empower the unit. A real, platinum-corroding acid, aqua regia, is a mixture of nitric and hydrocloric acid.
Both of them involve water in their production.

There would be few downsides to this change. Gameplay would stay intact and changing the prose and the colour of the jet wouldn't require much effort.

Oh crap, that is acid? I have to worry about it shorting out units as a conductive liquid AND dissolving them? :P

Saktoth, it's acid but it's strongly implied to be plain water by the graphics and both in-game and manual descriptions? I think yellow-green would better communicate the idea of acid. :)

N2maniac, considering the robots are built for war destroying them with an arcing water jet isn't believable. Being hit by a jet is different from being submerged. Besides amphibious units are supposed to be completely waterproof so acid would be more fitting in that sense too.

Skasi, what are you trying to convey?

http://en.wikipedia.org/wiki/Water_jet_cutter

If you want it to not arc we can do that too.

If it's water, I think it needs to be non-arcing. Otherwise it doesn't look like it can damage steel at a distance. However, that would work like yet another laser like knorke said. By the way, the pressure required to create such a jet would be amazing. :)

Acid would seem sufficiently harmful without arcing. Knorke mentioned he would expect some damage over time. That is a fair point. I wouldn't mind personally if the damage was caused over a short time as it could lead to interesting gameplay. However, if it lacked that, I think it would be far less baffling than seeing the unit spray water. Regarding the intuitivity knorke mentioned, perhaps the acid production could be made more visible by making the unit produce bubbles around it.

If it not arc, it would get some AA capability, that would compensate the loss of being able to shot through wrecks.
A non-arcing Water jet cutter won't looks same as laser, cause its particle travel speed is limited, you would see horizontal arc when it is attacking a moving unit.

Since these robots are each about the size of a tree/house, it doesn't seem all that unreasonable to me that these huge water jets that travel the length of a street could do some damage.