Kenneth is filling a pot with water to boil some spaghetti. The pot can hold 18 liters of water before it overflows. So far, Kenneth has poured 3 liters of water into the pot.

To determine how many more liters of water Kenneth can pour into the pot without it overflowing, we start with the maximum capacity of the pot, which is 18 liters. Kenneth has already poured 3 liters into the pot.

Let \( x \) represent the additional liters of water Kenneth can pour. Therefore, the total amount of water in the pot after pouring \( x \) more liters would be:

\[ 3 + x \]

To ensure the pot does not overflow, this total must be less than or equal to the pot's capacity (18 liters). We can express this relationship with the following inequality:

\[ 3 + x \leq 18 \]

This inequality describes the problem, indicating that Kenneth can pour in more water as long as the total does not exceed 18 liters.