Go to a school pool on weekends = 0 yen

The school my kid goes opens its pool on weekends in summer season. Residents can use the pool without charge. Unfortunately they open it only 3 weekends this year. My son went to the pool with his friends on last Sunday. The rule of usage is relatively strict rather than other private pools, for instance, swimmers have to wear their swim cap. (Swim cap is not necessary to wear in common pools.) The guards watch you to make sure you wash yourself before entering the pool. 

leaflet of open pool announcement