Why is there water under my refrigerator?

The reasoning behind that

Look at the water itself. If it is clear and appearing at the front, the line feeding the ice maker or dispenser has let go at a fitting. If it looks cloudy and there is a sheet of ice across the freezer floor, the defrost drain has frozen closed and the melt is backing up inside the cabinet. In Mission Hills the supply line deserves suspicion first, because in a house of this age that line was almost always added later, run a long way in narrow tubing, and often connected with a saddle valve that weeps rather than bursts.

How the diagnosis goes

The reason we would rather hear about this today than next week has little to do with the appliance. Water that gets under a built-in has nowhere to go and no air moving over it. It runs along the floor beneath the unit and into the toe-kick, and if the floor under yours is original hardwood or period tile bedded in mortar, the damage overtakes the cost of the repair quickly. Refinishing a section of floor that runs continuously into the rest of the house is a far bigger job than replacing a drain heater.

You can narrow it down before we arrive. Open the grille above the doors, where the machine compartment and the water connection sit on a full-height built-in, and look for a wet fitting or a damp line; that points at the supply side. Then open the freezer and look at the floor under the bottom basket, because a smooth sheet of ice there means the drain is blocked and the tray beneath is overflowing. If both are dry and the water only appears at the front on humid mornings, it may be condensation from a gasket that has stopped sealing, which is a door adjustment rather than a leak.

If that matches what yours is doing, say so when you call — it decides which parts come on the van.