Found this info here, Douglas Heineman:

6. Swimming Pools - Swimming pools must comply with all local ordinances (perimeter fencing, covers, etc.).

• Swimming pools must be operational to provide Contributory Value.
• The appraiser must report readily observable defects in a non-covered pool that would render the pool inoperable or unusable.
• If the pool water contains algae and is aesthetically unappealing, but  not otherwise contaminated, no cleaning is required.
• The appraiser must require that pools with unstable sides or structural issues be repaired or permanently filled in accordance with local guidelines, and the surrounding land re-graded if necessary.
• If the swimming pool has been winterized, or the appraiser cannot determine if the pool is in working order, the appraiser is to complete the appraisal with the extraordinary assumption that  the pool and its equipment can be restored to full operating condition at normal costs.

Hope this helps!

You should ask an appraiser. Are you an appraiser? If you are why are you asking here? If you're not, you shouldn't be appraising.

You have some good responses here.  

Kenneth J. Jones, Associate Broker nailed this one!

Looks like some good answers here already.

SEE Debe Maxwell, CRS 

Debe Maxwell, CRS has provided you with information that will help you.

Debe Maxwell, CRS for the win!

Unlike Kermit, they can't be green

Douglas Heineman Debe Maxwell, CRS has this one.

Good question. Most often they are assigned a value less than replacement cost.

I like the answer by Debe Maxwell, CRS. 

there are many appraisers here, and I'm confident they'll chime in with an answer....

Needing guarding rail from kids falling into. Need to be operational. 

No idea. 

Did you find a good answer?

In Denver we don't have many pools, so have had had to figure value.

Looks like you have some good answers here.

I believe this varies by region.

I agree with Kenneth.

Douglas Heineman - not done in a while for sure...

Not sure but they will let you know.