I do not know what the code said at time your project was first constructed, and you haven't stated the project location in order to determine applicable code. But for sake of discussion, let's assume the current 2022 LA Building Code Chapter 31B, which is adopted by the California Dept. of Public Health, applies to your project. It's probably also safe to assume that if it is a statewide health code requirement, it may apply to other jurisdictions unless those jurisdictions adopted a different or more stringent code.
2022 LABC Chapter 31B states the following regard (a) showers, (b) dressing facilities, and (c) toilet facilities.
Chapter 31B [DPH] Public Pools
Section 3116B Dressing, Shower and Toilet Facilities
Shower and dressing facilities shall be provided for users of a pool.
Exceptions:
1. Shower and dressing facilities may not be required when pool users have access to such facilities in adjacent living quarters.
2. Public toilet facilities may be omitted when pool users have access to toilet facilities either in living quarters located not more than 300 feet (91,440 mm) in travel distance from the pool or in an adjacent building such as a recreational facility, club-house or cabana.
3116B.2 Number of Sanitary Facilities
For the purpose of this subsection, one pool user shall be considered for every 15 square feet (1.39 m2) of pool water surface area and/or spray ground splash zone area.
3116B.2.1 Showers
One shower shall be provided for every 50 pool users.
3116B.2.2 Toilets
Separate toilet facilities shall be provided for each sex. One toilet shall be provided for every 60 women or less and one toilet plus one urinal for every 75 men or less.
3116B.2.3 Lavatories
One lavatory shall be provided for every 80 pool users.
The code does not have a specific definition of “adjacent” when referring to "adjacent living quarters". So the final requirement may be subjective on a case-by-case interpretive basis for a specific individual development, rather than a "bright line" prescriptive rule.
One more note, is that the apartment unit is not 10-20 residence where you have a short distance to walk. We have 13 buildings and are a distance away.
It is interesting to note that for toilets, 3116.B.1 exc. #2 limits “adjacent” to a 300’ travel distance, but for shower facilities there is no corresponding limit of distance.
From this, you need to determine and propose to the Authority Having Jurisdiction whether the apartments are sufficiently “adjacent” in terms of both spatial relationship and practical distance that the apartment showers and toilets fulfill the scoping requirements of LABC 3116.1.
Reminder, the above info has been provided as a hypothetical example. If your pool was built a long time ago under a different code, then that older code may be applicable instead of the 2022 LABC 31B code I quoted above.