To find the rate of the canoe when the water is still, we can use the given information:

1. **Distance downstream**: 72 km
2. **Time to travel downstream**: 2.4 hours
3. **Rate upstream**: 26 km/h

**Step 1: Calculate the downstream speed.**

The speed for downstream can be found using the formula:

\[
\text{Speed} = \frac{\text{Distance}}{\text{Time}}
\]

Substituting the known values:

\[
\text{Speed downstream} = \frac{72 \text{ km}}{2.4 \text{ h}} = 30 \text{ km/h}
\]

**Step 2: Set up the equations for speeds.**

Let \( r \) be the rate of the canoe in still water (km/h) and \( c \) be the speed of the current (km/h). Then we have:

\[
\text{Rate downstream} = r + c = 30 \text{ km/h} \quad (1)
\]
\[
\text{Rate upstream} = r - c = 26 \text{ km/h} \quad (2)
\]

**Step 3: Solve the equations.**

From equation (1):

\[
r + c = 30
\]

From equation (2):

\[
r - c = 26
\]

Now, we can add equations (1) and (2):

\[
(r + c) + (r - c) = 30 + 26
\]
\[
2r = 56
\]
\[
r = 28 \text{ km/h}
\]

**Conclusion:**

The rate of the canoe when the water is still is **28 km/h**.