Water strategy for silver

Tank - Soak Damage
Off-Tank/DPS - Soak Damage and DPS
DPS - Magic or Close Range Archer or Melee with Opportunity/Sneak. In our off-meta deck this can be also a "protected slot" for important troops like Demented Shark in melee only games
Utility/DPS - This can be a healer or another DPS
DPS/Utility - This is another flexible slot, usually with archers
Off-Tank/DPS - This last slot main role is to protect from Sneak and ideally dish out damage
Lets now look at great cheap troops for the different roles

Tank
In Water we have lots of amazing tanks.

Great usually cheap picks are:

Sea Monster - This is okay even at lvl1, lvl3 or lvl4 is the cheap alternative i would personally go for lvl5. Lvl6 which we can't play in Silver is where it shines but we cant use it...
Frozen Soldier - Lvl3 for budget, Lvl4 is the cap for silver. Once again at lvl5 which we cant play would be even better
Serpent of Eld - Lvl 4 is great especially if using Brighton as summoner
Kelp Initiate - Lvl 3 for cleanse. This is not so useful in this off-meta build (it's a must-have in the mage meta build). I personally rarely use him
Battle Ora - cheap choice for low mana games
Spineback Turtle - Excellent Option at lvl5 with 2 attacks and thorns
You can of course also use neutrals like Goblin Mech.
As mentioned we have plenty of options. you don't need all of these you should just pick the ones you like the most.
If i were to pick 2 i would go for Sea Monster (all games except low mana) and Spineback Turtle (low mana)