Swimming pools are great, but most people can't afford them or don't have access to one year-round, while it's a cinch to go out and walk when the urge strikes. Even when you're not in the mood, it's not as easy to talk yourself out of a walk as the idea of putting on trunks and going to find space in a crowded pool for a half-hour. I exercise in the pool every day for 45-60 minutes. What matters most when using weights is that you know the proper techniques and how many repetitions to do and how often. But using weights in the pool might be overkill.
Water already provides that extra resistance.
Add some steam. Travel farther, jump higher, pull harder. The larger the surface area moving through water, the more resistance. Think of your limbs as levers and extend them. Frontal kicks underwater are more difficult than knee lifts because the leg is longer when kicking.