Is amusement park water rides clean?

In theory, amusement park water rides are "Clean"  by clean I am assuming you are referring to sanitary.  All commercial pools and water parks are required to maintain and check their chemical residual levels multiple times a day, and most are even automatic, so in terms of them being clean and sanitized, you are pretty safe.  However, the health department does not monitor them every day (usually monthly or quarterly), so at some level it is the responsibility of the operator to make sure they maintain their sanitation.   I would assess the balance of the facility for cleanliness and maintenance to gauge the overall sanitation of the park.  In general, the larger, big name parks are chemically treated and safe and well maintained.  The loss of revenue from a breakout of E coli, can be devastating, and they know it.