There is water in the reservoir and it is frozen. there should be coolant in there, what should i do?

Sounds like you have either a leaking intake manifold gasket or a leaking head gasket... either way.. its time for a Qualified Professional...

Check the water pump and see if coolant is around it.

Any fault, defect, or blockage to the following components:
radiator fan (electrical or belt driven), water pump, coolant reservoir, radiator cap, thermostat, heater or radiator cores, by pass hoses, upper an lower radiator hoses, electrical and/or vacuum controls, blower fan, fuses, thermostat switch, low coolant levels or Improper coolant to water ratio, cracked cylinder heads, partially plugged or frozen engine block, or air pockets in the system.

So the level keeps dropping in the reservoir? If you have to keep adding coolant to the reservoir, the system is leaking or losing coolant somewhere. Have the system pressure tested to find the leak. Is the reservoir itself leaking? When the level gets low enough, first the reservoir will go dry, then the radiator level will start to drop.
Here's how the reservoir works: coolant is under pressure from the radiator cap seal. As coolant heats up from hot engine, it expands, and pressure forces the radiator cap seal up, coolant is forced into the reservoir-remember the hot mark on the reservoir? When car is shut off, coolant contracts, creating a vacuum in top of radiator. This vacuum works to suction coolant back from reservoir into the radiator, keeping the radiator topped up, and coolant should now be at the lower cold mark on the reservoir. It is a closed, sealed system. The only loss of coolant will be a very small amount of evaporation from the reservoir. If coolant level keeps dropping, there is a leak somewhere.

You can buy a 50/50 mix of coolant and water. Use that. And dont use tap water it can hurt your engine. If your loosing coolant check all your hoses for leaks and your reservoir for leaks.

Check the coolant reservoir tank and fill if needed. Most modern cars have a plastic reservoir of coolant connected to the top of the radiator. This will allow you to see if your coolant is low. Many have marks indicating the proper level of coolant when the engine is hot. Check to see if the coolant is at that level.
Add coolant (or water, in a pinch) to your reservoir to the full/hot line. On most cars, you can add liquid to your reservoir even if the car is hot. Check the owner's manual to be sure, or wait for the car to cool before opening.
If your car only has a radiator and no coolant reservoir, you must wait for it to cool before checking the level of coolant.

WAIT UNTIL YOUR ENGINE IS COLD,YOUR RADIATOR PRESSURE CAP IS LOCATED ON THE COOLANT OVER FLOW RESERVOIR, THATS WHERE YOU ADD COOLANT WHEN COOLANT LOW,YOU POUR COOLANT IN THE OVER FLOW RESERVOIR UNTIL COOLANT LEVEL REMAIN AT FULL COLD MARK DONT OVER FILL OVER FLOW RESERVOIR, WHEN COOLANT LEVEL STOP DROPPING WHEN ADDING COOLANT AND COOLANT LEVEL STAY AT COLD MARK ON THE RESERVOIR YOU RADIATOR HAS THE CORRECT COOLANT LEVEL IF COOLANT LEVEL KEEP DROPPING CHECK FOR COOLANT LEAKS AROUND RADIATOR AND THE TOP AND BOTTOM RADIATOR HOSES, LOOK FOR COOLANT LEAK AT WATER PUMP GASKET OR SEAL OR LEAK AT WATER PUMP WEEP HOLE IF YES REPLACE WATER PUMP.

Did you check the water pump? The hose should be firm when you cold start the vehicle since the thermostat is not open. Once the thermostat opens the coolant will flow provided the thermostat is working and installed in the correct orientation. Make sure the pulley for the water pump is turning and not frozen.

The radiator is that flat panel shaped object in the front-most center of the engine compartment. You don't add coolant and water directly into the radiator. On the right side of the engine compartment is a plastic overflow reservoir with a blue cap. That's where the coolant/water mix goes. Run the engine while adding coolant and water. There are fill marks on the reservoir indicating how much coolant/water mix is required. With the engine running, if the radiator is very low on coolant it will repeatedly draw fluid from the reservoir. Continue to add coolant/water mix until the situation stabilizes and the reservoir is filled to the high fill mark.

please rate, thx Coolant Recovery System NOTE: When the water thermostat (8575) is closed, there is no flow through the radiator coolant recovery reservoir (8A080).

Trapped air in the cooling system must be removed. A pressurized radiator coolant recovery reservoir system is used which continuously separates the air from the cooling system.

• When the water thermostat is open, coolant flows through the small hose from the top of the radiator outlet tank to the radiator coolant recovery reservoir.
• The radiator coolant recovery reservoir separates any trapped air from the coolant and replenishes the system through its radiator coolant recovery hose to the water thermostat housing.
• The radiator coolant recovery reservoir serves as the location for:
  • service fill
  • coolant expansion during warm-up
  • system pressurization from the pressure relief cap and
  • air separation during operation
• The radiator coolant recovery reservoir is designed to have approximately 0.5-1 liter (0.53-1.06 quarts) of air when cold to allow for coolant expansion.