Pool Slides - I would love a modular pool slide set/kit that could be combined with walls/floors/stairs/ladders/columns etc to build basic/small to complex/huge water slides and water parks.
Pool Waterfalls - We need at least 2 versions: Natural looking with rocks and artificial looking made from tiles, bricks, stone and concrete/adobe. Sims should be able to play, shower, kiss and woohoo under them (we have some of these animations already from IL). Waterfall could also have colours be changed via lighting settings.
Flexible Diving Boards - Wooden plank, modern metal and plastic finishes.
Social Pool Games/Activities - Hold breath, Marco Polo, throw and dive for dive sticks/quoits (+ dogs with C&D, + Diving skill with IL), push sims in, throw sims while in water, swim under legs, synchronised swimming (like group dancing).
Snorkeling - Enabled on pools with IL installed.
Water Sports - Swimming races, all boats working in pools (if large enough), water polo, octopush etc.
Pool Motion Generator - Can create waves (aesthetics/surfing/bodyboarding), currents (movement for floaties or balls on surface) etc.
Pool Effects BB - Similar to pond effects, but things appropriate to pools or giant aquariums such as fish, surface debris, wavelets etc.
Pool Maintenance - Pools have to be cleaned, filters need repairing/upgrading/cleaning, covered or heated in winter, chemicals added or rebalanced. Sims can do these things themselves or hire staff (Butler/Maid/Handyman) to do it for them.
Pool Parties Event - Host at homes or any venue with pool. Swimwear dress code (or venue dress code option on community lots). Whims for pool parties in summer or on hot days. Tasks could involve pool games, pool pranks, pool objects, food and drink, socialising, dancing, hot tubs/grilling if at location etc.
Waterpark Venue - Combined Pool, Park and Fairground type venue.
ETA: Typos.