Mkay, have your foci give +2 Water Offensive Control and +1 Water Offensive Power. That brings all attack Water evocations to +6.* As far as your spell, I suggest an Orbius remake.
Ice Cube
Type: Offensive Water Block, Adjucated as a Grapple
Power: 6 Shifts (4 Conviction, +1 Specialization, +1 Foci), 3 Effect, 3 Duration
Control: 6 (4 Discipline, +2 Foci)
Duration: 3 Exchanges
Opposed By: Dodge, Counterspell, Endurance if trapped, Armor Ineffective.
Targetting: Target in LoS
1 Mental Stress
Effect: The target is trapped in a magical block of ice, simulataneously being crushed and frozen. Every round, the target must roll Endurance against a +3. Failing the roll gives them a +1 Stress hit due to suffocation/being crushed, etc.
You can modify it how you want, making it weaker or stronger the way you see fit. Remember that you can add more shifts of effect later in the fight, letting you make it last longer if needed.
*If you really wanted to, you could have the foci give another +1 Power and +1 Control. However, said foci would only be useable with this specific Rote. You would use your one Focus Item slot, and the free one provided if you tie a foci to a single rote, which makes it useless for any spell but this one. I would go with using the one foci slot you have left as a +1 Water Defensive Control, so that you could have a Five shift Defensive Block for your other rote.