How to waterproof an interior basement cinderblock wall

Kills water seal. U can get at walmart

They sell a product called Drylok at the big box stores. Its a rubberized paint. Follow instructions.

Before you go to all the work of waterproofing the cinderblock... you need to determine where the water or moisture is coming from: are there cracks in the joints between blocks? is the exterior waterproofing compromised? do you need to install or repair "weeping tile"? Has something in your or your neighbor's yard changed to direct water toward your exterior walls or foundation? Do you need to add a dehumidifier to your heat/cooling HVAC system? HomeAdvisor.com or Angieslist.com can help you find a verified professional to give you an assessment of the problem... and how to fix it the first time.

If all you need is to paint the cinderblock... most large home improvement stores carry the products for that.

There are special paints on the market to resolve your issue. Check at your local hardware or paint store for the right product.

https://www.diynetwork.com/how-to/rooms-and-spaces/walls-and-ceilings/how-to-waterproof-a-cinderblock-wall

If your basement cinder wall is damp, you need to tackle this problem from the outside, not wait until the water has seeped inside. If you just seal the cement blocks inside, the water will still erode the cement from the outside. There are various ways to do this. Use your search engine to decide.

Inside I would use Drylok applied with a brush. https://www.youtube.com/watch?v=v4BPuil3S2o

But if you have a lot of water this might not be a total solution, you may need to install a French Drain and waterproof the outside of the building with liquid rubber... https://www.youtube.com/watch?v=RosQjZ3-Alo