It is maybe hard to believe but there are actually places where you can do water sports activity around Jakarta. Here is a list of activities as an inspiration for your weekend activity:
There are several popular rafting spots accessible from Jakarta, with most of them located in Sukabumi. Citarik river is the most famous, located in Cikadang Subdistrict of Sukabumi. You can choose from 5, 9, 12, or 17 km of rafting path, and would in total take from 2 to 5 hours. There is also the Citatih River, the popular grade 3+ rapids for whitewater rafting adventure in West Java. There are plenty of tour operators that can organize daily or overnight rafting tours, complete with meals and additional activities, bu for starters, check out Cherokee Adventure, Arus Liar or Niagara Arung Jeram.
For wakeboarding junkies, head to Epic Cablepark in Ancol Dreamland. Technically, it is not just wakeboarding, as it also incorporates skating as you will be pulled by a large towing mechanism (instead of a motorboat) around an area, going through a series of ramps and obstacles. Prices start from Rp. 125,000 per 2 hours or 250,000 for one whole day.
3. Jet Ski
If you feel like speeding on water, Jet Ski is one option. Ancol bay area has some spots where you can rent Jet Skis by the hour. Prices range from 500,000 to 1 million per hour. If you want cleaner water, you need to head out a little further west to Anyer beach, where you can rent the jet skis for as short as 15 minutes, for Rp. 200,000. Another option is to go to one of the Seribu Islands, such as Pulai Macan or Pulau Bidadari where you can ride jet skis in considerably better water.