The probability that a water pistol works properly is 92% or 0.92.

The probability that all n water pistols work properly is given by:

\(P(0) = (0.92)^n\)

We want the probability that at least one does not work properly to be greater than 0.9:

\(1 - P(0) > 0.9\)

Substituting for \(P(0)\):

\(1 - (0.92)^n > 0.9\)

Rearranging gives:

\((0.92)^n < 0.1\)

Taking logarithms on both sides:

\(n \log(0.92) < \log(0.1)\)

Solving for \(n\):

\(n > \frac{\log(0.1)}{\log(0.92)}\)

Calculating gives:

\(n > 27.6\)

Since \(n\) must be an integer, the smallest possible value is:

28