Calculate the amount of water used by the Soduku family from 13 June to 14 July 2025.

The meter reading on 14 July 2025 was 1321 kL.
The meter reading on 13 June 2025 was 1235 kL.

The amount of water used is $\boxed{\text{86 kL}}$.

2.1.2 Verify whether Mr Soduku's claim is valid.

Mr Soduku claims the bill for the month will be R1 200. We need to calculate the actual cost for 86 kL of water based on the provided tariff structure.

• First 6 kL: $6 \text{ kL}$ at 904 cents/kL
• Next 4 kL (from 7 to 10 kL): $4 \text{ kL}$ at 1027 cents/kL
• Next 10 kL (from 11 to 20 kL): $10 \text{ kL}$ at 1335 cents/kL
• Remaining kL (above 20 kL): $86 \text{ kL} - (6+4+10) \text{ kL} = 86 \text{ kL} - 20 \text{ kL} = 66 \text{ kL}$ at 1639 cents/kL

• Cost for first 6 kL: $6 \times 904 = 5424$ cents
• Cost for next 4 kL: $4 \times 1027 = 4108$ cents
• Cost for next 10 kL: $10 \times 1335 = 13350$ cents
• Cost for remaining 66 kL: $66 \times 1639 = 108174$ cents

Since $1 \text{ Rand} = 100 \text{ cents}$:

Mr Soduku claims the bill will be R1 200.
The calculated bill is R1 310.56.
Since R1 310.56 is not equal to R1 200, Mr Soduku's claim is not valid.

Mr Soduku's claim is $\boxed{\text{not valid}}$.