How to countering Zeus?

Get a Magic Stick or wand and make sure your whole team. Zeus spams his abilities, so being nearby means you get charges. Always carries Town Portal Scroll. This is good advice, but it is great advice vs. Zeus. Often he'll use his Thundergod's Wrath as soon as it is off cooldown if there has been a fight and people on your team are low, so when low Town Portal back to the fountain, heal up before he ults, and top off after and get back into the action right away.

A few things beat zeus.

First, rotations early

Seriously, from levels 1-4 he will lose to most lv 2 supports in a man fight. He has no escape only average HP, and is extremely reliant on rune control or Bottle crow to get anything out of mid. A Zeus who died in lane is going to be at a major level disadvantage which really cripples the hero.

Second, good initiation

Nyx Assassin, Bounty Hunter, Puck with Blink, anyone that can get in and burst him down early. Zeus THRIVES on long team fights where he can get off his nukes on cooldown. Seriously, a lv 7 Zeus with Null Talisman, Arcane Boots, Magic Wand, Bottle and full mana can deal well over 2500 damage over a 20 second team fight without even counting his passive. Get up in his face early and burst him down FAST or he will take out your entire team.

Get a fast Mekansm and everyone on the team should have a wand

People will tell you to rush Pipe of Insight, but IMO it is only a late game item for once Zeus has Aghanim's Scepter + Refresher Orb. The Pipe of Insight shield is calculated before magic resist, so the 400HP shield is really only protecting you from 300 damage. On the other hand, 250 HP from Mekansm can heals any kind of damage and it provides the team with extra armor. Be sure to use the Mekansm early though. If everyone was in range of Zeus' passive when he casts his first  Arc Lightning > Lightning Bolt > Arc Lightning, you should just use the Mekansm right there. If you don't you could very quickly end up with a situation where everyone is at ~75%HP, suddenly Zeus ultis and now everyone is under half and running away. If you Mekansm early, they stay at 60-70%, Zeus blew his full load, and your team can still man up and fight.