Water level in toilets

I am having problems with the water levels in both of my toilets. The water levels are lower than normal; because of this low level it is not always possible to flush the toilets effectively. When they are flushed they may work properly or may simply add more water to the toilet bowl but does not flush.
What is causing this?

By the way I do have my own septic system and leach lines.

Thank you Steve

Since both toilets seem to have the same problem, I would suspect there is clog in the main drain line or at the septic tank. (essential the same thing) When was the septic tank last pumped?

Gary Swart said:

Since both toilets seem to have the same problem, I would suspect there is clog in the main drain line or at the septic tank. (essential the same thing) When was the septic tank last pumped?

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I am not sure when the last time the septic tank was pumped out. You mentioned a clogged line; how would you recommend to unclogged the line?

Thanks for the help, Steve

Take a bucket of water and SLOWLY add it to the bowl. DOes the water come up and STAY up? Normally, a toilet bowl is overfilled, and the excess runs down the drain shortly after the refill is finished. By adding water slowly to the bowl, you should be able to determine the maximum water the bowl can hold.

Also, make sure that the refill hose in the tank is still pointing into the overflow tube. If it isn't, then it is just filling the tank, and not the bowl.

level

You do not differentiate between not enough water in the bowl to start with, or there is enough but then the level drops. Two different problems with multiple different answers.