This is a question I often hear from parents new to swimming. You will sometimes hear swimmers and their parents refer to a pool being fast. And at certain meets you might notice that some of the faster swimmers don't even bother to signup even though the pool might be less than a mile from their home.
A warmer pool will cause swimmers to over heat. Cooler water is considered faster, because it helps the body stay cool, especially during longer distance events. Colder water is also thought to be denser than warmer water, meaning each stroke your hand is able to get a better grip on the water. Pool temperature 75F to 78F is ideal.
Yes you read that right. Water can have different densities depending on what chemicals are used, and how much air is being suspended in it. A really clean pool you can stand on the blocks look down and not even be able to tell where the surface of the water is. A dirty pool the water will appear cloudy. The cloudiness is typically air suspended in the water. This causes you to slip water when you pull meaning your getting the full power out of each stroke.
A deeper pool is faster, as it helps to better absorb waves.
Skinny lane ropes do less to help absorb waves than larger lane ropes. When I went to Zones back in the 90s. the 50M indoor pool had double jumbo lane ropes between the lanes, which really helped eliminate waves.
Deeper gutters allow the walls to help better swallow up and absorb waves, especially on flip turns.
This is one of the most overlooked things that make a pool fast. Most newer pools built in the last 20 years have good ventilation systems, allowing for plenty of fresh air and more importantly Oxygen, but older pools were not built with that in mind. So once you have 100+ swimmers in the pool area, plus their parents and friends in the stands, the temperature rises, and the oxygen levels start to drop. Takes your average high school pool and makes it feel like you are swimming at altitude.
If you see the newer starting blocks with the adjustable ramp on the back for your foot to push against, those are faster. Swimmers are able to push themselves forward faster than the traditional starting blocks which have a semi rough tilted surface.
I have seen parents sign their kids up for every meet available, to the point were it feels like every weekend they are swimming in a meet. Unless you are just trying to get some first time swims done( 500 free, 200, fly, 400 IM), sometimes its better to just hold off for the meets at faster pools. It can be demotivating for kids who after a couple weeks of hard training to swim slower, just because the pool is slow. Better to focus on training than trying to do a 1 day tapper for every local swim meet held at the ancient HS pool with terrible air quality. This is something faster swimmers have figured out, and this is why you don't see them at every local swim meet.